[ios] Rename sessionID to snapshotID in //ios/c/b/snapshots

It is time to remove the use of the term "session" in
//ios/chrome/browser/snapshots.

The identifier used to store and retrieve images from SnapshotCache
is called |snapshotID|. The SnapshotCache has no concept of a Tab
or WebState. It is merely a collection of images with identifiers.

However, SnapshotTabHelper and SnapshotGenerator are tied to a
WebState. Within those classes, the unique identifier for a WebState
is called |tabID|. When those classes call SnapshotCache, they use
the WebState's |tabID| as the identifier to be used in SnapshotCache.

Change-Id: Ic08cd0d70b66e4d699bf06c8b5d8afc093e90255
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2354807
Commit-Queue: edchin <edchin@chromium.org>
Reviewed-by: Mohammad Refaat <mrefaat@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799782}

ios/chrome/browser/snapshots/snapshot_cache.h

@@ -23,36 +23,36 @@
 // only a singleton instance.
 @property(nonatomic, copy) NSString* uniqueIdentifier;
 
-// Track session IDs to not release on low memory and to reload on
+// Track snapshot IDs to not release on low memory and to reload on
 // |UIApplicationDidBecomeActiveNotification|.
 @property(nonatomic, strong) NSSet* pinnedIDs;
 
 // The scale that should be used for snapshots.
 - (CGFloat)snapshotScaleForDevice;
 
-// Retrieve a cached snapshot for the |sessionID| and return it via the callback
-// if it exists. The callback is guaranteed to be called synchronously if the
-// image is in memory. It will be called asynchronously if the image is on disk
-// or with nil if the image is not present at all.
-- (void)retrieveImageForSessionID:(NSString*)sessionID
+// Retrieve a cached snapshot for the |snapshotID| and return it via the
+// callback if it exists. The callback is guaranteed to be called synchronously
+// if the image is in memory. It will be called asynchronously if the image is
+// on disk or with nil if the image is not present at all.
+- (void)retrieveImageForSnapshotID:(NSString*)snapshotID
                           callback:(void (^)(UIImage*))callback;
 
-// Request the session's grey snapshot. If the image is already loaded in
+// Request the grey snapshot for |snapshotID|. If the image is already loaded in
 // memory, this will immediately call back on |callback|.
-- (void)retrieveGreyImageForSessionID:(NSString*)sessionID
+- (void)retrieveGreyImageForSnapshotID:(NSString*)snapshotID
                               callback:(void (^)(UIImage*))callback;
 
-- (void)setImage:(UIImage*)img withSessionID:(NSString*)sessionID;
+- (void)setImage:(UIImage*)image withSnapshotID:(NSString*)snapshotID;
 
 // Removes the image from both the LRU and disk cache, unless it is marked for
 // deferred deletion. Images marked for deferred deletion can only be removed by
 // calling |-removeMarkedImages|.
-- (void)removeImageWithSessionID:(NSString*)sessionID;
+- (void)removeImageWithSnapshotID:(NSString*)snapshotID;
 
 // Marks an image for deferred deletion. The image will not be immediately
-// deleted when |-removeImageWithSessionID:| is called. Images marked for
+// deleted when |-removeImageWithSnapshotID:| is called. Images marked for
 // deferred deletion can only be removed by calling |-removeMarkedImages|.
-- (void)markImageWithSessionID:(NSString*)sessionID;
+- (void)markImageWithSnapshotID:(NSString*)snapshotID;
 
 // Removes all marked images from both the LRU and disk cache.
 - (void)removeMarkedImages;
@@ -62,28 +62,28 @@
 - (void)unmarkAllImages;
 
 // Purge the cache of snapshots that are older than |date|. The snapshots for
-// the sessions given in |liveSessionIds| will be kept. This will be done
-// asynchronously on a background thread.
+// |liveSnapshotIDs| will be kept. This will be done asynchronously on a
+// background thread.
 - (void)purgeCacheOlderThan:(const base::Time&)date
-                    keeping:(NSSet*)liveSessionIds;
-// Hint that the snapshot for |sessionID| will likely be saved to disk when the
+                    keeping:(NSSet*)liveSnapshotIDs;
+// Hint that the snapshot for |snapshotID| will likely be saved to disk when the
 // application is backgrounded.  The snapshot is then saved in memory, so it
 // does not need to be read off disk.
-- (void)willBeSavedGreyWhenBackgrounding:(NSString*)sessionID;
+- (void)willBeSavedGreyWhenBackgrounding:(NSString*)snapshotID;
 
 // Create temporary cache of grey images for tablet side swipe.
-- (void)createGreyCache:(NSArray*)sessionIDs;
+- (void)createGreyCache:(NSArray*)snapshotIDs;
 // Release all images in grey cache.
 - (void)removeGreyCache;
-// Request the session's grey snapshot. If the image is already loaded this will
-// immediately call back on |callback|. Otherwise, only use |callback| for the
-// most recent caller. The callback is not guaranteed to be called.
-- (void)greyImageForSessionID:(NSString*)sessionID
+// Request the grey snapshot for |snapshotID|. If the image is already loaded
+// this will immediately call back on |callback|. Otherwise, only use |callback|
+// for the most recent caller. The callback is not guaranteed to be called.
+- (void)greyImageForSnapshotID:(NSString*)snapshotID
                       callback:(void (^)(UIImage*))callback;
 
-// Write a grey copy of the snapshot for |sessionID| to disk, but if and only if
-// a color version of the snapshot already exists in memory or on disk.
-- (void)saveGreyInBackgroundForSessionID:(NSString*)sessionID;
+// Write a grey copy of the snapshot for |snapshotID| to disk, but if and only
+// if a color version of the snapshot already exists in memory or on disk.
+- (void)saveGreyInBackgroundForSnapshotID:(NSString*)snapshotID;
 
 // Adds an observer to this snapshot cache.
 - (void)addObserver:(id<SnapshotCacheObserver>)observer;
@@ -99,8 +99,8 @@
 
 // Additionnal methods that should only be used for tests.
 @interface SnapshotCache (TestingAdditions)
-- (BOOL)hasImageInMemory:(NSString*)sessionID;
-- (BOOL)hasGreyImageInMemory:(NSString*)sessionID;
+- (BOOL)hasImageInMemory:(NSString*)snapshotID;
+- (BOOL)hasGreyImageInMemory:(NSString*)snapshotID;
 - (NSUInteger)lruCacheMaxSize;
 @end
 

ios/chrome/browser/snapshots/snapshot_cache.mm

@@ -48,21 +48,7 @@
 // List of observers to be notified of changes to the snapshot cache.
 @property(nonatomic, strong) SnapshotCacheObservers* observers;
 // Marked set of identifiers for which images should not be immediately deleted.
-@property(nonatomic, strong) NSMutableSet* markedIDs;
-
-// Remove all UIImages from |lruCache_|.
-- (void)handleEnterBackground;
-// Remove all but adjacent UIImages from |lruCache_|.
-- (void)handleLowMemory;
-// Restore adjacent UIImages to |lruCache_|.
-- (void)handleBecomeActive;
-// Clear most recent caller information.
-- (void)clearGreySessionInfo;
-// Load uncached snapshot image and convert image to grey.
-- (void)loadGreyImageAsync:(NSString*)sessionID;
-// Save grey image to |greyImageDictionary_| and call into most recent
-// |mostRecentGreyBlock_| if |mostRecentGreySessionId_| matches |sessionID|.
-- (void)saveGreyImage:(UIImage*)greyImage forKey:(NSString*)sessionID;
+@property(nonatomic, strong) NSMutableSet<NSString*>* markedIDs;
 @end
 
 namespace {
@@ -100,13 +86,13 @@ bool GetSnapshotsCacheDirectory(base::FilePath* snapshots_cache_directory) {
   return true;
 }
 
-// Returns the path of the image for |session_id|, in |cache_directory|,
+// Returns the path of the image for |snapshot_id|, in |cache_directory|,
 // of type |image_type| and scale |image_scale|.
-base::FilePath ImagePath(NSString* session_id,
+base::FilePath ImagePath(NSString* snapshot_id,
                          ImageType image_type,
                          ImageScale image_scale,
                          const base::FilePath& cache_directory) {
-  NSString* filename = session_id;
+  NSString* filename = snapshot_id;
   switch (image_type) {
     case IMAGE_TYPE_COLOR:
       // no-op
@@ -153,7 +139,7 @@ CGFloat ScaleFromImageScale(ImageScale image_scale) {
   }
 }
 
-UIImage* ReadImageForSessionFromDisk(NSString* session_id,
+UIImage* ReadImageForSnapshotIDFromDisk(NSString* snapshot_id,
                                         ImageType image_type,
                                         ImageScale image_scale,
                                         const base::FilePath& cache_directory) {
@@ -162,7 +148,7 @@ UIImage* ReadImageForSessionFromDisk(NSString* session_id,
   // reporting the image as damaged https://stackoverflow.com/q/5081297/5353
   // are fixed.
   base::FilePath file_path =
-      ImagePath(session_id, image_type, image_scale, cache_directory);
+      ImagePath(snapshot_id, image_type, image_scale, cache_directory);
   NSString* path = base::SysUTF8ToNSString(file_path.AsUTF8Unsafe());
   base::ScopedBlockingCall scoped_blocking_call(FROM_HERE,
                                                 base::BlockingType::WILL_BLOCK);
@@ -207,20 +193,20 @@ void WriteImageToDisk(UIImage* image, const base::FilePath& file_path) {
   }
 }
 
-void ConvertAndSaveGreyImage(NSString* session_id,
+void ConvertAndSaveGreyImage(NSString* snapshot_id,
                              ImageScale image_scale,
                              UIImage* color_image,
                              const base::FilePath& cache_directory) {
   base::ScopedBlockingCall scoped_blocking_call(FROM_HERE,
                                                 base::BlockingType::WILL_BLOCK);
   if (!color_image) {
-    color_image = ReadImageForSessionFromDisk(session_id, IMAGE_TYPE_COLOR,
+    color_image = ReadImageForSnapshotIDFromDisk(snapshot_id, IMAGE_TYPE_COLOR,
                                                  image_scale, cache_directory);
     if (!color_image)
       return;
   }
   UIImage* grey_image = GreyImage(color_image);
-  WriteImageToDisk(grey_image, ImagePath(session_id, IMAGE_TYPE_GREYSCALE,
+  WriteImageToDisk(grey_image, ImagePath(snapshot_id, IMAGE_TYPE_GREYSCALE,
                                          image_scale, cache_directory));
 }
 
@@ -236,14 +222,14 @@ void ConvertAndSaveGreyImage(NSString* session_id,
   // is called.
   NSMutableDictionary<NSString*, UIImage*>* _greyImageDictionary;
 
-  // Session ID of most recent pending grey snapshot request.
-  NSString* _mostRecentGreySessionId;
+  // Snapshot ID of most recent pending grey snapshot request.
+  NSString* _mostRecentGreySnapshotID;
   // Block used by pending request for a grey snapshot.
   void (^_mostRecentGreyBlock)(UIImage*);
 
-  // Session ID and corresponding UIImage for the snapshot that will likely
+  // Snapshot ID and corresponding UIImage for the snapshot that will likely
   // be requested to be saved to disk when the application is backgrounded.
-  NSString* _backgroundingImageSessionId;
+  NSString* _backgroundingSnapshotID;
   UIImage* _backgroundingColorImage;
 
   // Scale for snapshot images. May be smaller than the screen scale in order
@@ -341,13 +327,13 @@ void ConvertAndSaveGreyImage(NSString* session_id,
   return ScaleFromImageScale(_snapshotsScale);
 }
 
-- (void)retrieveImageForSessionID:(NSString*)sessionID
+- (void)retrieveImageForSnapshotID:(NSString*)snapshotID
                           callback:(void (^)(UIImage*))callback {
   DCHECK_CALLED_ON_VALID_SEQUENCE(_sequenceChecker);
-  DCHECK(sessionID);
+  DCHECK(snapshotID);
   DCHECK(callback);
 
-  if (UIImage* image = [_lruCache objectForKey:sessionID]) {
+  if (UIImage* image = [_lruCache objectForKey:snapshotID]) {
     callback(image);
     return;
   }
@@ -365,46 +351,46 @@ void ConvertAndSaveGreyImage(NSString* session_id,
   base::PostTaskAndReplyWithResult(
       _taskRunner.get(), FROM_HERE, base::BindOnce(^UIImage*() {
         // Retrieve the image on a high priority thread.
-        return ReadImageForSessionFromDisk(sessionID, IMAGE_TYPE_COLOR,
+        return ReadImageForSnapshotIDFromDisk(snapshotID, IMAGE_TYPE_COLOR,
                                               snapshotsScale, cacheDirectory);
       }),
       base::BindOnce(^(UIImage* image) {
         if (image)
-          [weakLRUCache setObject:image forKey:sessionID];
+          [weakLRUCache setObject:image forKey:snapshotID];
         callback(image);
       }));
 }
 
-- (void)setImage:(UIImage*)image withSessionID:(NSString*)sessionID {
+- (void)setImage:(UIImage*)image withSnapshotID:(NSString*)snapshotID {
   DCHECK_CALLED_ON_VALID_SEQUENCE(_sequenceChecker);
-  if (!image || !sessionID || !_taskRunner)
+  if (!image || !snapshotID || !_taskRunner)
     return;
 
-  [_lruCache setObject:image forKey:sessionID];
+  [_lruCache setObject:image forKey:snapshotID];
 
-  [self.observers snapshotCache:self didUpdateSnapshotForIdentifier:sessionID];
+  [self.observers snapshotCache:self didUpdateSnapshotForIdentifier:snapshotID];
 
   // Copy ivars used by the block so that it does not reference |self|.
   const base::FilePath cacheDirectory = _cacheDirectory;
   const ImageScale snapshotsScale = _snapshotsScale;
 
   // Save the image to disk.
-  _taskRunner->PostTask(
-      FROM_HERE, base::BindOnce(^{
-        WriteImageToDisk(image, ImagePath(sessionID, IMAGE_TYPE_COLOR,
+  _taskRunner->PostTask(FROM_HERE, base::BindOnce(^{
+                          WriteImageToDisk(
+                              image, ImagePath(snapshotID, IMAGE_TYPE_COLOR,
                                                snapshotsScale, cacheDirectory));
                         }));
 }
 
-- (void)removeImageWithSessionID:(NSString*)sessionID {
+- (void)removeImageWithSnapshotID:(NSString*)snapshotID {
   DCHECK_CALLED_ON_VALID_SEQUENCE(_sequenceChecker);
   // Do not immediately delete if the ID is marked.
-  if ([self.markedIDs containsObject:sessionID])
+  if ([self.markedIDs containsObject:snapshotID])
     return;
 
-  [_lruCache removeObjectForKey:sessionID];
+  [_lruCache removeObjectForKey:snapshotID];
 
-  [self.observers snapshotCache:self didUpdateSnapshotForIdentifier:sessionID];
+  [self.observers snapshotCache:self didUpdateSnapshotForIdentifier:snapshotID];
 
   if (!_taskRunner)
     return;
@@ -416,21 +402,21 @@ void ConvertAndSaveGreyImage(NSString* session_id,
   _taskRunner->PostTask(
       FROM_HERE, base::BindOnce(^{
         for (size_t index = 0; index < base::size(kImageTypes); ++index) {
-          base::DeleteFile(ImagePath(sessionID, kImageTypes[index],
+          base::DeleteFile(ImagePath(snapshotID, kImageTypes[index],
                                      snapshotsScale, cacheDirectory));
         }
       }));
 }
 
-- (void)markImageWithSessionID:(NSString*)sessionID {
-  [self.markedIDs addObject:sessionID];
+- (void)markImageWithSnapshotID:(NSString*)snapshotID {
+  [self.markedIDs addObject:snapshotID];
 }
 
 - (void)removeMarkedImages {
   while (self.markedIDs.count > 0) {
-    NSString* sessionID = [self.markedIDs anyObject];
-    [self.markedIDs removeObject:sessionID];
-    [self removeImageWithSessionID:sessionID];
+    NSString* snapshotID = [self.markedIDs anyObject];
+    [self.markedIDs removeObject:snapshotID];
+    [self removeImageWithSnapshotID:snapshotID];
   }
 }
 
@@ -438,18 +424,18 @@ void ConvertAndSaveGreyImage(NSString* session_id,
   [self.markedIDs removeAllObjects];
 }
 
-- (base::FilePath)imagePathForSessionID:(NSString*)sessionID {
-  return ImagePath(sessionID, IMAGE_TYPE_COLOR, _snapshotsScale,
+- (base::FilePath)imagePathForSnapshotID:(NSString*)snapshotID {
+  return ImagePath(snapshotID, IMAGE_TYPE_COLOR, _snapshotsScale,
                    _cacheDirectory);
 }
 
-- (base::FilePath)greyImagePathForSessionID:(NSString*)sessionID {
-  return ImagePath(sessionID, IMAGE_TYPE_GREYSCALE, _snapshotsScale,
+- (base::FilePath)greyImagePathForSnapshotID:(NSString*)snapshotID {
+  return ImagePath(snapshotID, IMAGE_TYPE_GREYSCALE, _snapshotsScale,
                    _cacheDirectory);
 }
 
 - (void)purgeCacheOlderThan:(const base::Time&)date
-                    keeping:(NSSet*)liveSessionIds {
+                    keeping:(NSSet*)liveSnapshotIDs {
   DCHECK_CALLED_ON_VALID_SEQUENCE(_sequenceChecker);
 
   if (!_taskRunner)
@@ -468,9 +454,9 @@ void ConvertAndSaveGreyImage(NSString* session_id,
           return;
 
         std::set<base::FilePath> filesToKeep;
-        for (NSString* sessionID : liveSessionIds) {
+        for (NSString* snapshotID : liveSnapshotIDs) {
           for (size_t index = 0; index < base::size(kImageTypes); ++index) {
-            filesToKeep.insert(ImagePath(sessionID, kImageTypes[index],
+            filesToKeep.insert(ImagePath(snapshotID, kImageTypes[index],
                                          snapshotsScale, cacheDirectory));
           }
         }
@@ -490,57 +476,64 @@ void ConvertAndSaveGreyImage(NSString* session_id,
       }));
 }
 
-- (void)willBeSavedGreyWhenBackgrounding:(NSString*)sessionID {
+- (void)willBeSavedGreyWhenBackgrounding:(NSString*)snapshotID {
   DCHECK_CALLED_ON_VALID_SEQUENCE(_sequenceChecker);
-  if (!sessionID)
+  if (!snapshotID)
     return;
-  _backgroundingImageSessionId = [sessionID copy];
-  _backgroundingColorImage = [_lruCache objectForKey:sessionID];
+  _backgroundingSnapshotID = [snapshotID copy];
+  _backgroundingColorImage = [_lruCache objectForKey:snapshotID];
 }
 
+// Remove all but adjacent UIImages from |lruCache_|.
 - (void)handleLowMemory {
   DCHECK_CALLED_ON_VALID_SEQUENCE(_sequenceChecker);
   NSMutableDictionary<NSString*, UIImage*>* dictionary =
       [NSMutableDictionary dictionaryWithCapacity:2];
-  for (NSString* sessionID in self.pinnedIDs) {
-    UIImage* image = [_lruCache objectForKey:sessionID];
+  for (NSString* snapshotID in self.pinnedIDs) {
+    UIImage* image = [_lruCache objectForKey:snapshotID];
     if (image)
-      [dictionary setObject:image forKey:sessionID];
+      [dictionary setObject:image forKey:snapshotID];
   }
   [_lruCache removeAllObjects];
-  for (NSString* sessionID in self.pinnedIDs)
-    [_lruCache setObject:[dictionary objectForKey:sessionID] forKey:sessionID];
+  for (NSString* snapshotID in self.pinnedIDs)
+    [_lruCache setObject:[dictionary objectForKey:snapshotID]
+                  forKey:snapshotID];
 }
 
+// Remove all UIImages from |lruCache_|.
 - (void)handleEnterBackground {
   DCHECK_CALLED_ON_VALID_SEQUENCE(_sequenceChecker);
   [_lruCache removeAllObjects];
 }
 
+// Restore adjacent UIImages to |lruCache_|.
 - (void)handleBecomeActive {
   DCHECK_CALLED_ON_VALID_SEQUENCE(_sequenceChecker);
-  for (NSString* sessionID in self.pinnedIDs)
-    [self retrieveImageForSessionID:sessionID
+  for (NSString* snapshotID in self.pinnedIDs)
+    [self retrieveImageForSnapshotID:snapshotID
                             callback:^(UIImage*){
                             }];
 }
 
-- (void)saveGreyImage:(UIImage*)greyImage forKey:(NSString*)sessionID {
+// Save grey image to |greyImageDictionary_| and call into most recent
+// |_mostRecentGreyBlock| if |_mostRecentGreySnapshotID| matches |snapshotID|.
+- (void)saveGreyImage:(UIImage*)greyImage forSnapshotID:(NSString*)snapshotID {
   DCHECK_CALLED_ON_VALID_SEQUENCE(_sequenceChecker);
   if (greyImage)
-    [_greyImageDictionary setObject:greyImage forKey:sessionID];
-  if ([sessionID isEqualToString:_mostRecentGreySessionId]) {
+    [_greyImageDictionary setObject:greyImage forKey:snapshotID];
+  if ([snapshotID isEqualToString:_mostRecentGreySnapshotID]) {
     _mostRecentGreyBlock(greyImage);
-    [self clearGreySessionInfo];
+    [self clearGreySnapshotInfo];
   }
 }
 
-- (void)loadGreyImageAsync:(NSString*)sessionID {
+// Load uncached snapshot image and convert image to grey.
+- (void)loadGreyImageAsync:(NSString*)snapshotID {
   DCHECK_CALLED_ON_VALID_SEQUENCE(_sequenceChecker);
-  // Don't call -retrieveImageForSessionID here because it caches the colored
+  // Don't call -retrieveImageForSnapshotID here because it caches the colored
   // image, which we don't need for the grey image cache. But if the image is
   // already in the cache, use it.
-  UIImage* image = [_lruCache objectForKey:sessionID];
+  UIImage* image = [_lruCache objectForKey:snapshotID];
 
   if (!_taskRunner)
     return;
@@ -555,62 +548,63 @@ void ConvertAndSaveGreyImage(NSString* session_id,
         // If the image is not in the cache, load it from disk.
         UIImage* localImage = image;
         if (!localImage) {
-          localImage = ReadImageForSessionFromDisk(
-              sessionID, IMAGE_TYPE_COLOR, snapshotsScale, cacheDirectory);
+          localImage = ReadImageForSnapshotIDFromDisk(
+              snapshotID, IMAGE_TYPE_COLOR, snapshotsScale, cacheDirectory);
         }
         if (localImage)
           localImage = GreyImage(localImage);
         return localImage;
       }),
       base::BindOnce(^(UIImage* greyImage) {
-        [weakSelf saveGreyImage:greyImage forKey:sessionID];
+        [weakSelf saveGreyImage:greyImage forSnapshotID:snapshotID];
       }));
 }
 
-- (void)createGreyCache:(NSArray*)sessionIDs {
+- (void)createGreyCache:(NSArray*)snapshotIDs {
   DCHECK_CALLED_ON_VALID_SEQUENCE(_sequenceChecker);
   _greyImageDictionary =
       [NSMutableDictionary dictionaryWithCapacity:kGreyInitialCapacity];
-  for (NSString* sessionID in sessionIDs)
-    [self loadGreyImageAsync:sessionID];
+  for (NSString* snapshotID in snapshotIDs)
+    [self loadGreyImageAsync:snapshotID];
 }
 
 - (void)removeGreyCache {
   DCHECK_CALLED_ON_VALID_SEQUENCE(_sequenceChecker);
   _greyImageDictionary = nil;
-  [self clearGreySessionInfo];
+  [self clearGreySnapshotInfo];
 }
 
-- (void)clearGreySessionInfo {
+// Clear most recent caller information.
+- (void)clearGreySnapshotInfo {
   DCHECK_CALLED_ON_VALID_SEQUENCE(_sequenceChecker);
-  _mostRecentGreySessionId = nil;
+  _mostRecentGreySnapshotID = nil;
   _mostRecentGreyBlock = nil;
 }
 
-- (void)greyImageForSessionID:(NSString*)sessionID
+- (void)greyImageForSnapshotID:(NSString*)snapshotID
                       callback:(void (^)(UIImage*))callback {
   DCHECK_CALLED_ON_VALID_SEQUENCE(_sequenceChecker);
   DCHECK(_greyImageDictionary);
-  DCHECK(sessionID);
+  DCHECK(snapshotID);
   DCHECK(callback);
 
-  if (UIImage* image = [_greyImageDictionary objectForKey:sessionID]) {
+  if (UIImage* image = [_greyImageDictionary objectForKey:snapshotID]) {
     callback(image);
-    [self clearGreySessionInfo];
+    [self clearGreySnapshotInfo];
   } else {
-    _mostRecentGreySessionId = [sessionID copy];
+    _mostRecentGreySnapshotID = [snapshotID copy];
     _mostRecentGreyBlock = [callback copy];
   }
 }
 
-- (void)retrieveGreyImageForSessionID:(NSString*)sessionID
+- (void)retrieveGreyImageForSnapshotID:(NSString*)snapshotID
                               callback:(void (^)(UIImage*))callback {
   DCHECK_CALLED_ON_VALID_SEQUENCE(_sequenceChecker);
-  DCHECK(sessionID);
+  DCHECK(snapshotID);
   DCHECK(callback);
 
   if (_greyImageDictionary) {
-    if (UIImage* image = [_greyImageDictionary objectForKey:sessionID]) {
+    if (UIImage* image = [_greyImageDictionary objectForKey:snapshotID]) {
       callback(image);
       return;
     }
@@ -629,7 +623,7 @@ void ConvertAndSaveGreyImage(NSString* session_id,
   base::PostTaskAndReplyWithResult(
       _taskRunner.get(), FROM_HERE, base::BindOnce(^UIImage*() {
         // Retrieve the image on a high priority thread.
-        return ReadImageForSessionFromDisk(sessionID, IMAGE_TYPE_GREYSCALE,
+        return ReadImageForSnapshotIDFromDisk(snapshotID, IMAGE_TYPE_GREYSCALE,
                                               snapshotsScale, cacheDirectory);
       }),
       base::BindOnce(^(UIImage* image) {
@@ -637,7 +631,7 @@ void ConvertAndSaveGreyImage(NSString* session_id,
           callback(image);
           return;
         }
-        [weakSelf retrieveImageForSessionID:sessionID
+        [weakSelf retrieveImageForSnapshotID:snapshotID
                                     callback:^(UIImage* localImage) {
                                       if (localImage)
                                         localImage = GreyImage(localImage);
@@ -646,15 +640,15 @@ void ConvertAndSaveGreyImage(NSString* session_id,
       }));
 }
 
-- (void)saveGreyInBackgroundForSessionID:(NSString*)sessionID {
+- (void)saveGreyInBackgroundForSnapshotID:(NSString*)snapshotID {
   DCHECK_CALLED_ON_VALID_SEQUENCE(_sequenceChecker);
-  if (!sessionID)
+  if (!snapshotID)
     return;
 
-  // The color image may still be in memory.  Verify the sessionID matches.
+  // The color image may still be in memory.  Verify the snapshotID matches.
   if (_backgroundingColorImage) {
-    if (![_backgroundingImageSessionId isEqualToString:sessionID]) {
-      _backgroundingImageSessionId = nil;
+    if (![_backgroundingSnapshotID isEqualToString:snapshotID]) {
+      _backgroundingSnapshotID = nil;
       _backgroundingColorImage = nil;
     }
   }
@@ -667,10 +661,10 @@ void ConvertAndSaveGreyImage(NSString* session_id,
   const base::FilePath cacheDirectory = _cacheDirectory;
   const ImageScale snapshotsScale = _snapshotsScale;
 
-  _taskRunner->PostTask(
-      FROM_HERE, base::BindOnce(^{
-        ConvertAndSaveGreyImage(sessionID, snapshotsScale,
-                                backgroundingColorImage, cacheDirectory);
+  _taskRunner->PostTask(FROM_HERE, base::BindOnce(^{
+                          ConvertAndSaveGreyImage(snapshotID, snapshotsScale,
+                                                  backgroundingColorImage,
+                                                  cacheDirectory);
                         }));
 }
 
@@ -690,12 +684,12 @@ void ConvertAndSaveGreyImage(NSString* session_id,
 
 @implementation SnapshotCache (TestingAdditions)
 
-- (BOOL)hasImageInMemory:(NSString*)sessionID {
-  return [_lruCache objectForKey:sessionID] != nil;
+- (BOOL)hasImageInMemory:(NSString*)snapshotID {
+  return [_lruCache objectForKey:snapshotID] != nil;
 }
 
-- (BOOL)hasGreyImageInMemory:(NSString*)sessionID {
-  return [_greyImageDictionary objectForKey:sessionID] != nil;
+- (BOOL)hasGreyImageInMemory:(NSString*)snapshotID {
+  return [_greyImageDictionary objectForKey:snapshotID] != nil;
 }
 
 - (NSUInteger)lruCacheMaxSize {

ios/chrome/browser/snapshots/snapshot_cache_internal.h

@@ -14,10 +14,10 @@ class FilePath;
 @class NSString;
 
 @interface SnapshotCache (Internal)
-// Returns filepath to the color snapshot of |sessionID|.
-- (base::FilePath)imagePathForSessionID:(NSString*)sessionID;
-// Returns filepath to the greyscale snapshot of |sessionID|.
-- (base::FilePath)greyImagePathForSessionID:(NSString*)sessionID;
+// Returns filepath to the color snapshot of |snapshotID|.
+- (base::FilePath)imagePathForSnapshotID:(NSString*)snapshotID;
+// Returns filepath to the greyscale snapshot of |snapshotID|.
+- (base::FilePath)greyImagePathForSnapshotID:(NSString*)snapshotID;
 @end
 
 #endif  // IOS_CHROME_BROWSER_SNAPSHOTS_SNAPSHOT_CACHE_INTERNAL_H_

ios/chrome/browser/snapshots/snapshot_cache_unittest.mm

@@ -27,7 +27,7 @@
 #error "This file requires ARC support."
 #endif
 
-static const NSUInteger kSessionCount = 10;
+static const NSUInteger kSnapshotCount = 10;
 static const NSUInteger kSnapshotPixelSize = 8;
 
 @interface FakeSnapshotCacheObserver : NSObject<SnapshotCacheObserver>
@@ -46,13 +46,13 @@ namespace {
 
 class SnapshotCacheTest : public PlatformTest {
  protected:
-  // Build an array of session names and an array of UIImages filled with
+  // Build an array of snapshot IDs and an array of UIImages filled with
   // random colors.
   void SetUp() override {
     PlatformTest::SetUp();
     snapshotCache_ = [[SnapshotCache alloc] init];
-    testImages_ = [[NSMutableArray alloc] initWithCapacity:kSessionCount];
-    testSessions_ = [[NSMutableArray alloc] initWithCapacity:kSessionCount];
+    testImages_ = [[NSMutableArray alloc] initWithCapacity:kSnapshotCount];
+    snapshotIDs_ = [[NSMutableArray alloc] initWithCapacity:kSnapshotCount];
 
     CGFloat scale = [snapshotCache_ snapshotScaleForDevice];
     UIGraphicsBeginImageContextWithOptions(
@@ -60,11 +60,11 @@ class SnapshotCacheTest : public PlatformTest {
     CGContextRef context = UIGraphicsGetCurrentContext();
     srand(1);
 
-    for (NSUInteger i = 0; i < kSessionCount; ++i) {
+    for (NSUInteger i = 0; i < kSnapshotCount; ++i) {
       UIImage* image = GenerateRandomImage(context);
       [testImages_ addObject:image];
-      [testSessions_
-          addObject:[NSString stringWithFormat:@"SessionId-%" PRIuNS, i]];
+      [snapshotIDs_
+          addObject:[NSString stringWithFormat:@"SnapshotID-%" PRIuNS, i]];
     }
 
     UIGraphicsEndImageContext();
@@ -113,26 +113,26 @@ class SnapshotCacheTest : public PlatformTest {
   void ClearDumpedImages() {
     SnapshotCache* cache = GetSnapshotCache();
 
-    NSString* sessionID;
-    for (sessionID in testSessions_)
-      [cache removeImageWithSessionID:sessionID];
+    NSString* snapshotID;
+    for (snapshotID in snapshotIDs_)
+      [cache removeImageWithSnapshotID:snapshotID];
 
     FlushRunLoops();
-    // The above calls to -removeImageWithSessionID remove both the color
-    // and grey snapshots for each sessionID, if they are on disk.  However,
+    // The above calls to -removeImageWithSnapshotID remove both the color
+    // and grey snapshots for each snapshotID, if they are on disk.  However,
     // ensure we also get rid of the grey snapshots in memory.
     [cache removeGreyCache];
 
     __block BOOL foundImage = NO;
     __block NSUInteger numCallbacks = 0;
-    for (sessionID in testSessions_) {
-      base::FilePath path([cache imagePathForSessionID:sessionID]);
+    for (snapshotID in snapshotIDs_) {
+      base::FilePath path([cache imagePathForSnapshotID:snapshotID]);
 
       // Checks that the snapshot is not on disk.
       EXPECT_FALSE(base::PathExists(path));
 
       // Check that the snapshot is not in the dictionary.
-      [cache retrieveImageForSessionID:sessionID
+      [cache retrieveImageForSnapshotID:snapshotID
                                callback:^(UIImage* image) {
                                  ++numCallbacks;
                                  if (image)
@@ -142,14 +142,14 @@ class SnapshotCacheTest : public PlatformTest {
 
     // Expect that all the callbacks ran and that none retrieved an image.
     FlushRunLoops();
-    EXPECT_EQ([testSessions_ count], numCallbacks);
+    EXPECT_EQ([snapshotIDs_ count], numCallbacks);
     EXPECT_FALSE(foundImage);
   }
 
-  // Loads kSessionCount color images into the cache.  If |waitForFilesOnDisk|
+  // Loads kSnapshotCount color images into the cache.  If |waitForFilesOnDisk|
   // is YES, will not return until the images have been written to disk.
   void LoadAllColorImagesIntoCache(bool waitForFilesOnDisk) {
-    LoadColorImagesIntoCache(kSessionCount, waitForFilesOnDisk);
+    LoadColorImagesIntoCache(kSnapshotCount, waitForFilesOnDisk);
   }
 
   // Loads |count| color images into the cache.  If |waitForFilesOnDisk|
@@ -160,28 +160,28 @@ class SnapshotCacheTest : public PlatformTest {
     for (NSUInteger i = 0; i < count; ++i) {
       @autoreleasepool {
         UIImage* image = [testImages_ objectAtIndex:i];
-        NSString* sessionID = [testSessions_ objectAtIndex:i];
-        [cache setImage:image withSessionID:sessionID];
+        NSString* snapshotID = [snapshotIDs_ objectAtIndex:i];
+        [cache setImage:image withSnapshotID:snapshotID];
       }
     }
     if (waitForFilesOnDisk) {
       FlushRunLoops();
       for (NSUInteger i = 0; i < count; ++i) {
         // Check that images are on the disk.
-        NSString* sessionID = [testSessions_ objectAtIndex:i];
-        base::FilePath path([cache imagePathForSessionID:sessionID]);
+        NSString* snapshotID = [snapshotIDs_ objectAtIndex:i];
+        base::FilePath path([cache imagePathForSnapshotID:snapshotID]);
         EXPECT_TRUE(base::PathExists(path));
       }
     }
   }
 
-  // Waits for the first |count| grey images for sessions in |testSessions_|
-  // to be placed in the cache.
+  // Waits for the first |count| grey images for |snapshotIDs_| to be placed in
+  // the cache.
   void WaitForGreyImagesInCache(NSUInteger count) {
     SnapshotCache* cache = GetSnapshotCache();
     FlushRunLoops();
     for (NSUInteger i = 0; i < count; i++)
-      EXPECT_TRUE([cache hasGreyImageInMemory:testSessions_[i]]);
+      EXPECT_TRUE([cache hasGreyImageInMemory:snapshotIDs_[i]]);
   }
 
   // Guesses the order of the color channels in the image.
@@ -227,7 +227,7 @@ class SnapshotCacheTest : public PlatformTest {
 
   web::WebTaskEnvironment task_environment_;
   SnapshotCache* snapshotCache_;
-  NSMutableArray* testSessions_;
+  NSMutableArray* snapshotIDs_;
   NSMutableArray* testImages_;
 };
 
@@ -237,22 +237,22 @@ class SnapshotCacheTest : public PlatformTest {
 TEST_F(SnapshotCacheTest, Cache) {
   SnapshotCache* cache = GetSnapshotCache();
 
-  NSUInteger expectedCacheSize = MIN(kSessionCount, [cache lruCacheMaxSize]);
+  NSUInteger expectedCacheSize = MIN(kSnapshotCount, [cache lruCacheMaxSize]);
 
   // Put all images in the cache.
   for (NSUInteger i = 0; i < expectedCacheSize; ++i) {
     UIImage* image = [testImages_ objectAtIndex:i];
-    NSString* sessionID = [testSessions_ objectAtIndex:i];
-    [cache setImage:image withSessionID:sessionID];
+    NSString* snapshotID = [snapshotIDs_ objectAtIndex:i];
+    [cache setImage:image withSnapshotID:snapshotID];
   }
 
   // Get images back.
   __block NSUInteger numberOfCallbacks = 0;
   for (NSUInteger i = 0; i < expectedCacheSize; ++i) {
-    NSString* sessionID = [testSessions_ objectAtIndex:i];
+    NSString* snapshotID = [snapshotIDs_ objectAtIndex:i];
     UIImage* expectedImage = [testImages_ objectAtIndex:i];
     EXPECT_TRUE(expectedImage != nil);
-    [cache retrieveImageForSessionID:sessionID
+    [cache retrieveImageForSnapshotID:snapshotID
                              callback:^(UIImage* image) {
                                // Images have not been removed from the
                                // dictionnary. We expect the same pointer.
@@ -269,18 +269,18 @@ TEST_F(SnapshotCacheTest, SaveToDisk) {
   SnapshotCache* cache = GetSnapshotCache();
 
   // Put all images in the cache.
-  for (NSUInteger i = 0; i < kSessionCount; ++i) {
+  for (NSUInteger i = 0; i < kSnapshotCount; ++i) {
     UIImage* image = [testImages_ objectAtIndex:i];
-    NSString* sessionID = [testSessions_ objectAtIndex:i];
-    [cache setImage:image withSessionID:sessionID];
+    NSString* snapshotID = [snapshotIDs_ objectAtIndex:i];
+    [cache setImage:image withSnapshotID:snapshotID];
   }
   FlushRunLoops();
 
-  for (NSUInteger i = 0; i < kSessionCount; ++i) {
+  for (NSUInteger i = 0; i < kSnapshotCount; ++i) {
     // Check that images are on the disk.
-    NSString* sessionID = [testSessions_ objectAtIndex:i];
+    NSString* snapshotID = [snapshotIDs_ objectAtIndex:i];
 
-    base::FilePath path([cache imagePathForSessionID:sessionID]);
+    base::FilePath path([cache imagePathForSnapshotID:snapshotID]);
     EXPECT_TRUE(base::PathExists(path));
 
     // Check image colors by comparing the first pixel against the reference
@@ -327,39 +327,39 @@ TEST_F(SnapshotCacheTest, Purge) {
   SnapshotCache* cache = GetSnapshotCache();
 
   // Put all images in the cache.
-  for (NSUInteger i = 0; i < kSessionCount; ++i) {
+  for (NSUInteger i = 0; i < kSnapshotCount; ++i) {
     UIImage* image = [testImages_ objectAtIndex:i];
-    NSString* sessionID = [testSessions_ objectAtIndex:i];
-    [cache setImage:image withSessionID:sessionID];
+    NSString* snapshotID = [snapshotIDs_ objectAtIndex:i];
+    [cache setImage:image withSnapshotID:snapshotID];
   }
 
-  NSMutableSet* liveSessions = [NSMutableSet setWithCapacity:1];
-  [liveSessions addObject:[testSessions_ objectAtIndex:0]];
+  NSMutableSet* liveSnapshotIDs = [NSMutableSet setWithCapacity:1];
+  [liveSnapshotIDs addObject:[snapshotIDs_ objectAtIndex:0]];
 
   // Purge the cache.
   [cache purgeCacheOlderThan:(base::Time::Now() - base::TimeDelta::FromHours(1))
-                     keeping:liveSessions];
+                     keeping:liveSnapshotIDs];
   FlushRunLoops();
 
   // Check that nothing has been deleted.
-  for (NSUInteger i = 0; i < kSessionCount; ++i) {
+  for (NSUInteger i = 0; i < kSnapshotCount; ++i) {
     // Check that images are on the disk.
-    NSString* sessionID = [testSessions_ objectAtIndex:i];
+    NSString* snapshotID = [snapshotIDs_ objectAtIndex:i];
 
-    base::FilePath path([cache imagePathForSessionID:sessionID]);
+    base::FilePath path([cache imagePathForSnapshotID:snapshotID]);
     EXPECT_TRUE(base::PathExists(path));
   }
 
   // Purge the cache.
-  [cache purgeCacheOlderThan:base::Time::Now() keeping:liveSessions];
+  [cache purgeCacheOlderThan:base::Time::Now() keeping:liveSnapshotIDs];
   FlushRunLoops();
 
   // Check that the file have been deleted.
-  for (NSUInteger i = 0; i < kSessionCount; ++i) {
+  for (NSUInteger i = 0; i < kSnapshotCount; ++i) {
     // Check that images are on the disk.
-    NSString* sessionID = [testSessions_ objectAtIndex:i];
+    NSString* snapshotID = [snapshotIDs_ objectAtIndex:i];
 
-    base::FilePath path([cache imagePathForSessionID:sessionID]);
+    base::FilePath path([cache imagePathForSnapshotID:snapshotID]);
     if (i == 0)
       EXPECT_TRUE(base::PathExists(path));
     else
@@ -374,8 +374,8 @@ TEST_F(SnapshotCacheTest, HandleMemoryWarning) {
 
   SnapshotCache* cache = GetSnapshotCache();
 
-  NSString* firstPinnedID = [testSessions_ objectAtIndex:4];
-  NSString* secondPinnedID = [testSessions_ objectAtIndex:6];
+  NSString* firstPinnedID = [snapshotIDs_ objectAtIndex:4];
+  NSString* secondPinnedID = [snapshotIDs_ objectAtIndex:6];
   NSMutableSet* set = [NSMutableSet set];
   [set addObject:firstPinnedID];
   [set addObject:secondPinnedID];
@@ -386,7 +386,7 @@ TEST_F(SnapshotCacheTest, HandleMemoryWarning) {
   EXPECT_EQ(YES, [cache hasImageInMemory:firstPinnedID]);
   EXPECT_EQ(YES, [cache hasImageInMemory:secondPinnedID]);
 
-  NSString* notPinnedID = [testSessions_ objectAtIndex:2];
+  NSString* notPinnedID = [snapshotIDs_ objectAtIndex:2];
   EXPECT_FALSE([cache hasImageInMemory:notPinnedID]);
 
   // Wait for the final image to be pulled off disk.
@@ -404,22 +404,22 @@ TEST_F(SnapshotCacheTest, CreateGreyCache) {
 
   // Request the creation of a grey image cache for all images.
   SnapshotCache* cache = GetSnapshotCache();
-  [cache createGreyCache:testSessions_];
+  [cache createGreyCache:snapshotIDs_];
 
   // Wait for them to be put into the grey image cache.
-  WaitForGreyImagesInCache(kSessionCount);
+  WaitForGreyImagesInCache(kSnapshotCount);
 
   __block NSUInteger numberOfCallbacks = 0;
-  for (NSUInteger i = 0; i < kSessionCount; ++i) {
-    NSString* sessionID = [testSessions_ objectAtIndex:i];
-    [cache retrieveGreyImageForSessionID:sessionID
+  for (NSUInteger i = 0; i < kSnapshotCount; ++i) {
+    NSString* snapshotID = [snapshotIDs_ objectAtIndex:i];
+    [cache retrieveGreyImageForSnapshotID:snapshotID
                                  callback:^(UIImage* image) {
                                    EXPECT_TRUE(image);
                                    ++numberOfCallbacks;
                                  }];
   }
 
-  EXPECT_EQ(numberOfCallbacks, kSessionCount);
+  EXPECT_EQ(numberOfCallbacks, kSnapshotCount);
 }
 
 // Same as previous test, except that all the color images are on disk,
@@ -434,22 +434,22 @@ TEST_F(SnapshotCacheTest, CreateGreyCacheFromDisk) {
   TriggerMemoryWarning();
 
   // Request the creation of a grey image cache for all images.
-  [cache createGreyCache:testSessions_];
+  [cache createGreyCache:snapshotIDs_];
 
   // Wait for them to be put into the grey image cache.
-  WaitForGreyImagesInCache(kSessionCount);
+  WaitForGreyImagesInCache(kSnapshotCount);
 
   __block NSUInteger numberOfCallbacks = 0;
-  for (NSUInteger i = 0; i < kSessionCount; ++i) {
-    NSString* sessionID = [testSessions_ objectAtIndex:i];
-    [cache retrieveGreyImageForSessionID:sessionID
+  for (NSUInteger i = 0; i < kSnapshotCount; ++i) {
+    NSString* snapshotID = [snapshotIDs_ objectAtIndex:i];
+    [cache retrieveGreyImageForSnapshotID:snapshotID
                                  callback:^(UIImage* image) {
                                    EXPECT_TRUE(image);
                                    ++numberOfCallbacks;
                                  }];
   }
 
-  EXPECT_EQ(numberOfCallbacks, kSessionCount);
+  EXPECT_EQ(numberOfCallbacks, kSnapshotCount);
 }
 #endif  // !TARGET_IPHONE_SIMULATOR
 
@@ -460,11 +460,11 @@ TEST_F(SnapshotCacheTest, CreateGreyCacheFromDisk) {
 // Disabled due to the greyImage crash.  b/8048597
 TEST_F(SnapshotCacheTest, MostRecentGreyBlock) {
   const NSUInteger kNumImages = 3;
-  NSMutableArray* sessionIDs =
+  NSMutableArray* snapshotIDs =
       [[NSMutableArray alloc] initWithCapacity:kNumImages];
-  [sessionIDs addObject:[testSessions_ objectAtIndex:0]];
-  [sessionIDs addObject:[testSessions_ objectAtIndex:1]];
-  [sessionIDs addObject:[testSessions_ objectAtIndex:2]];
+  [snapshotIDs addObject:[snapshotIDs_ objectAtIndex:0]];
+  [snapshotIDs addObject:[snapshotIDs_ objectAtIndex:1]];
+  [snapshotIDs addObject:[snapshotIDs_ objectAtIndex:2]];
 
   SnapshotCache* cache = GetSnapshotCache();
 
@@ -475,21 +475,21 @@ TEST_F(SnapshotCacheTest, MostRecentGreyBlock) {
   TriggerMemoryWarning();
 
   // Enable the grey image cache.
-  [cache createGreyCache:sessionIDs];
+  [cache createGreyCache:snapshotIDs];
 
   // Request the grey versions
   __block BOOL firstCallbackCalled = NO;
   __block BOOL secondCallbackCalled = NO;
   __block BOOL thirdCallbackCalled = NO;
-  [cache greyImageForSessionID:[testSessions_ objectAtIndex:0]
+  [cache greyImageForSnapshotID:[snapshotIDs_ objectAtIndex:0]
                        callback:^(UIImage*) {
                          firstCallbackCalled = YES;
                        }];
-  [cache greyImageForSessionID:[testSessions_ objectAtIndex:1]
+  [cache greyImageForSnapshotID:[snapshotIDs_ objectAtIndex:1]
                        callback:^(UIImage*) {
                          secondCallbackCalled = YES;
                        }];
-  [cache greyImageForSessionID:[testSessions_ objectAtIndex:2]
+  [cache greyImageForSnapshotID:[snapshotIDs_ objectAtIndex:2]
                        callback:^(UIImage*) {
                          thirdCallbackCalled = YES;
                        }];
@@ -510,16 +510,16 @@ TEST_F(SnapshotCacheTest, GreyImageAllInBackground) {
   SnapshotCache* cache = GetSnapshotCache();
 
   // Now convert every image into a grey image, on disk, in the background.
-  for (NSUInteger i = 0; i < kSessionCount; ++i) {
-    [cache saveGreyInBackgroundForSessionID:[testSessions_ objectAtIndex:i]];
+  for (NSUInteger i = 0; i < kSnapshotCount; ++i) {
+    [cache saveGreyInBackgroundForSnapshotID:[snapshotIDs_ objectAtIndex:i]];
   }
 
-  // Waits for the grey images for the sessions in |testSessions_| to be written
-  // to disk, which happens in a background thread.
+  // Waits for the grey images for |snapshotIDs_| to be written to disk, which
+  // happens in a background thread.
   FlushRunLoops();
 
-  for (NSString* sessionID in testSessions_) {
-    base::FilePath path([cache greyImagePathForSessionID:sessionID]);
+  for (NSString* snapshotID in snapshotIDs_) {
+    base::FilePath path([cache greyImagePathForSnapshotID:snapshotID]);
     EXPECT_TRUE(base::PathExists(path));
     base::DeleteFile(path);
   }
@@ -540,17 +540,17 @@ TEST_F(SnapshotCacheTest, SizeAndScalePreservation) {
 
   // Add the image to the cache then call handle low memory to ensure the image
   // is read from disk instead of the in-memory cache.
-  NSString* const kSession = @"foo";
-  [cache setImage:image withSessionID:kSession];
+  NSString* const kSnapshotID = @"foo";
+  [cache setImage:image withSnapshotID:kSnapshotID];
   FlushRunLoops();  // ensure the file is written to disk.
   TriggerMemoryWarning();
 
   // Retrive the image and have the callback verify the size and scale.
   __block BOOL callbackComplete = NO;
-  [cache retrieveImageForSessionID:kSession
+  [cache
+      retrieveImageForSnapshotID:kSnapshotID
                         callback:^(UIImage* imageFromDisk) {
-                            EXPECT_EQ(image.size.width,
-                                      imageFromDisk.size.width);
+                          EXPECT_EQ(image.size.width, imageFromDisk.size.width);
                           EXPECT_EQ(image.size.height,
                                     imageFromDisk.size.height);
                           EXPECT_EQ(image.scale, imageFromDisk.scale);
@@ -576,33 +576,33 @@ TEST_F(SnapshotCacheTest, DeleteRetinaImages) {
 
   // Add the image to the cache then call handle low memory to ensure the image
   // is read from disk instead of the in-memory cache.
-  NSString* const kSession = @"foo";
-  [cache setImage:image withSessionID:kSession];
+  NSString* const kSnapshotID = @"foo";
+  [cache setImage:image withSnapshotID:kSnapshotID];
   FlushRunLoops();  // ensure the file is written to disk.
   TriggerMemoryWarning();
 
   // Verify the file was writted with @2x in the file name.
-  base::FilePath retinaFile = [cache imagePathForSessionID:kSession];
+  base::FilePath retinaFile = [cache imagePathForSnapshotID:kSnapshotID];
   EXPECT_TRUE(base::PathExists(retinaFile));
 
   // Delete the image.
-  [cache removeImageWithSessionID:kSession];
+  [cache removeImageWithSnapshotID:kSnapshotID];
   FlushRunLoops();  // ensure the file is removed.
 
   EXPECT_FALSE(base::PathExists(retinaFile));
 }
 
 // Tests that a marked image does not immediately delete when calling
-// |-removeImageWithSessionID:|. Calling |-removeMarkedImages| immediately
+// |-removeImageWithSnapshotID:|. Calling |-removeMarkedImages| immediately
 // deletes the marked image.
 TEST_F(SnapshotCacheTest, MarkedImageNotImmediatelyDeleted) {
   SnapshotCache* cache = GetSnapshotCache();
   UIImage* image =
       GenerateRandomImage(CGSizeMake(kSnapshotPixelSize, kSnapshotPixelSize));
-  [cache setImage:image withSessionID:@"sessionID"];
-  base::FilePath image_path = [cache imagePathForSessionID:@"sessionID"];
-  [cache markImageWithSessionID:@"sessionID"];
-  [cache removeImageWithSessionID:@"sessionID"];
+  [cache setImage:image withSnapshotID:@"snapshotID"];
+  base::FilePath image_path = [cache imagePathForSnapshotID:@"snapshotID"];
+  [cache markImageWithSnapshotID:@"snapshotID"];
+  [cache removeImageWithSnapshotID:@"snapshotID"];
   // Give enough time for deletion.
   FlushRunLoops();
   EXPECT_TRUE(base::PathExists(image_path));
@@ -617,9 +617,9 @@ TEST_F(SnapshotCacheTest, UnmarkedImageNotDeleted) {
   SnapshotCache* cache = GetSnapshotCache();
   UIImage* image =
       GenerateRandomImage(CGSizeMake(kSnapshotPixelSize, kSnapshotPixelSize));
-  [cache setImage:image withSessionID:@"sessionID"];
-  base::FilePath image_path = [cache imagePathForSessionID:@"sessionID"];
-  [cache markImageWithSessionID:@"sessionID"];
+  [cache setImage:image withSnapshotID:@"snapshotID"];
+  base::FilePath image_path = [cache imagePathForSnapshotID:@"snapshotID"];
+  [cache markImageWithSnapshotID:@"snapshotID"];
   [cache unmarkAllImages];
   [cache removeMarkedImages];
   // Give enough time for deletion.
@@ -635,12 +635,12 @@ TEST_F(SnapshotCacheTest, ObserversNotifiedOnSetAndRemoveImage) {
   [cache addObserver:observer];
   EXPECT_NSEQ(nil, observer.lastUpdatedIdentifier);
   UIImage* image = [testImages_ objectAtIndex:0];
-  NSString* sessionID = [testSessions_ objectAtIndex:0];
-  [cache setImage:image withSessionID:sessionID];
-  EXPECT_NSEQ(sessionID, observer.lastUpdatedIdentifier);
+  NSString* snapshotID = [snapshotIDs_ objectAtIndex:0];
+  [cache setImage:image withSnapshotID:snapshotID];
+  EXPECT_NSEQ(snapshotID, observer.lastUpdatedIdentifier);
   observer.lastUpdatedIdentifier = nil;
-  [cache removeImageWithSessionID:sessionID];
-  EXPECT_NSEQ(sessionID, observer.lastUpdatedIdentifier);
+  [cache removeImageWithSnapshotID:snapshotID];
+  EXPECT_NSEQ(snapshotID, observer.lastUpdatedIdentifier);
   [cache removeObserver:observer];
 }
 }  // namespace

ios/chrome/browser/snapshots/snapshot_generator.h

@@ -24,8 +24,7 @@ class WebState;
 
 // Designated initializer.
 - (instancetype)initWithWebState:(web::WebState*)webState
-               snapshotSessionId:(NSString*)snapshotSessionId
-    NS_DESIGNATED_INITIALIZER;
+                           tabID:(NSString*)tabID NS_DESIGNATED_INITIALIZER;
 
 - (instancetype)init NS_UNAVAILABLE;
 

ios/chrome/browser/snapshots/snapshot_generator.mm

@@ -56,7 +56,7 @@ BOOL ViewHierarchyContainsWKWebView(UIView* view) {
 @interface SnapshotGenerator ()<CRWWebStateObserver>
 
 // The unique ID for the web state.
-@property(nonatomic, copy) NSString* sessionID;
+@property(nonatomic, copy) NSString* tabID;
 
 // The associated web state.
 @property(nonatomic, assign) web::WebState* webState;
@@ -68,12 +68,12 @@ BOOL ViewHierarchyContainsWKWebView(UIView* view) {
 }
 
 - (instancetype)initWithWebState:(web::WebState*)webState
-               snapshotSessionId:(NSString*)snapshotSessionId {
+                           tabID:(NSString*)tabID {
   if ((self = [super init])) {
     DCHECK(webState);
-    DCHECK(snapshotSessionId);
+    DCHECK(tabID);
     _webState = webState;
-    _sessionID = snapshotSessionId;
+    _tabID = tabID;
 
     _webStateObserver = std::make_unique<web::WebStateObserverBridge>(self);
     _webState->AddObserver(_webStateObserver.get());
@@ -92,7 +92,7 @@ BOOL ViewHierarchyContainsWKWebView(UIView* view) {
 - (void)retrieveSnapshot:(void (^)(UIImage*))callback {
   DCHECK(callback);
   if (self.snapshotCache) {
-    [self.snapshotCache retrieveImageForSessionID:self.sessionID
+    [self.snapshotCache retrieveImageForSnapshotID:self.tabID
                                           callback:callback];
   } else {
     callback(nil);
@@ -114,7 +114,7 @@ BOOL ViewHierarchyContainsWKWebView(UIView* view) {
 
   SnapshotCache* snapshotCache = self.snapshotCache;
   if (snapshotCache) {
-    [snapshotCache retrieveGreyImageForSessionID:self.sessionID
+    [snapshotCache retrieveGreyImageForSnapshotID:self.tabID
                                          callback:wrappedCallback];
   } else {
     wrappedCallback(nil);
@@ -178,7 +178,7 @@ BOOL ViewHierarchyContainsWKWebView(UIView* view) {
 }
 
 - (void)removeSnapshot {
-  [self.snapshotCache removeImageWithSessionID:self.sessionID];
+  [self.snapshotCache removeImageWithSnapshotID:self.tabID];
 }
 
 #pragma mark - Private methods
@@ -277,10 +277,10 @@ BOOL ViewHierarchyContainsWKWebView(UIView* view) {
 // Updates the snapshot cache with |snapshot|.
 - (void)updateSnapshotCacheWithImage:(UIImage*)snapshot {
   if (snapshot) {
-    [self.snapshotCache setImage:snapshot withSessionID:self.sessionID];
+    [self.snapshotCache setImage:snapshot withSnapshotID:self.tabID];
   } else {
     // Remove any stale snapshot since the snapshot failed.
-    [self.snapshotCache removeImageWithSessionID:self.sessionID];
+    [self.snapshotCache removeImageWithSnapshotID:self.tabID];
   }
 }
 

ios/chrome/browser/snapshots/snapshot_tab_helper.h

@@ -30,9 +30,9 @@ class SnapshotTabHelper : public infobars::InfoBarManager::Observer,
   ~SnapshotTabHelper() override;
 
   // Creates the tab helper for |web_state| if it does not exists. The
-  // unique identifier |session_id| is used when interacting with the
+  // unique identifier |tab_id| is used when interacting with the
   // cache to save or fetch snapshots.
-  static void CreateForWebState(web::WebState* web_state, NSString* session_id);
+  static void CreateForWebState(web::WebState* web_state, NSString* tab_id);
 
   // Sets the delegate. Capturing snapshot before setting a delegate will
   // results in failures. The delegate is not owned by the tab helper.
@@ -81,7 +81,7 @@ class SnapshotTabHelper : public infobars::InfoBarManager::Observer,
  private:
   friend class web::WebStateUserData<SnapshotTabHelper>;
 
-  SnapshotTabHelper(web::WebState* web_state, NSString* session_id);
+  SnapshotTabHelper(web::WebState* web_state, NSString* tab_id);
 
   // web::WebStateObserver implementation.
   void PageLoaded(

ios/chrome/browser/snapshots/snapshot_tab_helper.mm

@@ -47,12 +47,12 @@ SnapshotTabHelper::~SnapshotTabHelper() {
 
 // static
 void SnapshotTabHelper::CreateForWebState(web::WebState* web_state,
-                                          NSString* session_id) {
+                                          NSString* tab_id) {
   DCHECK(web_state);
   if (!FromWebState(web_state)) {
     web_state->SetUserData(
         UserDataKey(),
-        base::WrapUnique(new SnapshotTabHelper(web_state, session_id)));
+        base::WrapUnique(new SnapshotTabHelper(web_state, tab_id)));
   }
 }
 
@@ -109,14 +109,13 @@ void SnapshotTabHelper::IgnoreNextLoad() {
   ignore_next_load_ = true;
 }
 
-SnapshotTabHelper::SnapshotTabHelper(web::WebState* web_state,
-                                     NSString* session_id)
+SnapshotTabHelper::SnapshotTabHelper(web::WebState* web_state, NSString* tab_id)
     : web_state_(web_state),
       web_state_observer_(this),
       infobar_observer_(this),
       weak_ptr_factory_(this) {
   snapshot_generator_ = [[SnapshotGenerator alloc] initWithWebState:web_state_
-                                                  snapshotSessionId:session_id];
+                                                              tabID:tab_id];
   web_state_observer_.Add(web_state_);
 
   // Supports missing InfoBarManager to make testing easier.

ios/chrome/browser/snapshots/snapshot_tab_helper_unittest.mm

@@ -86,9 +86,9 @@ class SnapshotTabHelperTest : public PlatformTest {
  public:
   SnapshotTabHelperTest() {
     // Create the SnapshotTabHelper with a fake delegate.
-    snapshot_session_id_ = [[NSUUID UUID] UUIDString];
+    snapshot_id_ = [[NSUUID UUID] UUIDString];
     delegate_ = [[TabHelperSnapshotGeneratorDelegate alloc] init];
-    SnapshotTabHelper::CreateForWebState(&web_state_, snapshot_session_id_);
+    SnapshotTabHelper::CreateForWebState(&web_state_, snapshot_id_);
     SnapshotTabHelper::FromWebState(&web_state_)->SetDelegate(delegate_);
 
     // Set custom snapshot cache.
@@ -106,7 +106,7 @@ class SnapshotTabHelperTest : public PlatformTest {
   ~SnapshotTabHelperTest() override { [snapshot_cache_ shutdown]; }
 
   void SetCachedSnapshot(UIImage* image) {
-    [snapshot_cache_ setImage:image withSessionID:snapshot_session_id_];
+    [snapshot_cache_ setImage:image withSnapshotID:snapshot_id_];
   }
 
   UIImage* GetCachedSnapshot() {
@@ -114,7 +114,7 @@ class SnapshotTabHelperTest : public PlatformTest {
     base::RunLoop* run_loop_ptr = &run_loop;
 
     __block UIImage* snapshot = nil;
-    [snapshot_cache_ retrieveImageForSessionID:snapshot_session_id_
+    [snapshot_cache_ retrieveImageForSnapshotID:snapshot_id_
                                        callback:^(UIImage* cached_snapshot) {
                                          snapshot = cached_snapshot;
                                          run_loop_ptr->Quit();
@@ -128,7 +128,7 @@ class SnapshotTabHelperTest : public PlatformTest {
   web::WebTaskEnvironment task_environment_;
   TabHelperSnapshotGeneratorDelegate* delegate_ = nil;
   SnapshotCache* snapshot_cache_ = nil;
-  NSString* snapshot_session_id_ = nil;
+  NSString* snapshot_id_ = nil;
   web::TestWebState web_state_;
 
  private:
@@ -340,14 +340,14 @@ TEST_F(SnapshotTabHelperTest, ClosingWebStateDoesNotRemoveSnapshot) {
 
   NSString* tab_id = TabIdTabHelper::FromWebState(web_state.get())->tab_id();
   SnapshotTabHelper::CreateForWebState(web_state.get(), tab_id);
-  [[partialMock reject] removeImageWithSessionID:tab_id];
+  [[partialMock reject] removeImageWithSnapshotID:tab_id];
 
   // Use @try/@catch as -reject raises an exception.
   @try {
     web_state.reset();
     EXPECT_OCMOCK_VERIFY(partialMock);
   } @catch (NSException* exception) {
-    // The exception is raised when -removeImageWithSessionID: is invoked. As
+    // The exception is raised when -removeImageWithSnapshotID: is invoked. As
     // this should not happen, mark the test as failed.
     GTEST_FAIL();
   }

ios/chrome/browser/tabs/tab_model.mm

@@ -295,7 +295,7 @@ void RecordInterfaceOrientationMetric() {
             ->tab_id();
 
     [_snapshotBrowserAgent->GetSnapshotCache()
-        saveGreyInBackgroundForSessionID:tabId];
+        saveGreyInBackgroundForSnapshotID:tabId];
   }
 }
 

ios/chrome/browser/ui/tab_grid/tab_grid_mediator.mm

@@ -308,7 +308,7 @@ web::WebState* GetWebStateWithId(WebStateList* web_state_list,
   for (int i = 0; i < self.webStateList->count(); i++) {
     web::WebState* webState = self.webStateList->GetWebStateAt(i);
     TabIdTabHelper* tabHelper = TabIdTabHelper::FromWebState(webState);
-    [self.snapshotCache markImageWithSessionID:tabHelper->tab_id()];
+    [self.snapshotCache markImageWithSnapshotID:tabHelper->tab_id()];
   }
   self.closedSessionWindow = SerializeWebStateList(self.webStateList);
   int old_size =