Enable the snapshot cache on iPad when the tab switcher is enabled.

BUG=576269

Review URL: https://codereview.chromium.org/1587663002

Cr-Commit-Position: refs/heads/master@{#369418}

ios/chrome/browser/snapshots/snapshot_cache.mm

@@ -144,15 +144,17 @@ void ConvertAndSaveGreyImage(
     DCHECK_CURRENTLY_ON_WEB_THREAD(web::WebThread::UI);
     propertyReleaser_SnapshotCache_.Init(self, [SnapshotCache class]);
 
-    if (!IsIPadIdiom()) {
-      if (experimental_flags::IsLRUSnapshotCacheEnabled()) {
-        lruCache_.reset(
-            [[LRUCache alloc] initWithCacheSize:kLRUCacheMaxCapacity]);
-      } else {
-        imageDictionary_.reset([[NSMutableDictionary alloc]
-            initWithCapacity:kCacheInitialCapacity]);
-      }
+    // Always use the LRUCache when the tab switcher is enabled.
+    if (experimental_flags::IsTabSwitcherEnabled() ||
+        experimental_flags::IsLRUSnapshotCacheEnabled()) {
+      lruCache_.reset(
+          [[LRUCache alloc] initWithCacheSize:kLRUCacheMaxCapacity]);
+    } else {
+      imageDictionary_.reset(
+          [[NSMutableDictionary alloc] initWithCapacity:kCacheInitialCapacity]);
+    }
 
+    if (!IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled()) {
       [[NSNotificationCenter defaultCenter]
           addObserver:self
              selector:@selector(handleLowMemory)
@@ -174,7 +176,7 @@ void ConvertAndSaveGreyImage(
 }
 
 - (void)dealloc {
-  if (!IsIPadIdiom()) {
+  if (!IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled()) {
     [[NSNotificationCenter defaultCenter]
         removeObserver:self
                   name:UIApplicationDidReceiveMemoryWarningNotification
@@ -207,9 +209,10 @@ void ConvertAndSaveGreyImage(
                          callback:(void (^)(UIImage*))callback {
   DCHECK_CURRENTLY_ON_WEB_THREAD(web::WebThread::UI);
   DCHECK(sessionID);
-  // iPad does not cache images, so if there is no callback we can avoid an
-  // expensive read from storage.
-  if (IsIPadIdiom() && !callback)
+
+  // Cache on iPad is enabled only when the tab switcher is enabled.
+  if ((IsIPadIdiom() && !experimental_flags::IsTabSwitcherEnabled()) &&
+      !callback)
     return;
 
   UIImage* img = nil;
@@ -233,10 +236,9 @@ void ConvertAndSaveGreyImage(
             [SnapshotCache imagePathForSessionID:sessionID]) retain]);
       }),
       base::BindBlock(^(base::scoped_nsobject<UIImage> image) {
-        // The iPad tab switcher is currently using its own memory cache so the
-        // image is not stored in memory here if running on iPad.
-        // The same logic is used on image writes (code below).
-        if (!IsIPadIdiom() && image) {
+        // Cache on iPad is enabled only when the tab switcher is enabled.
+        if ((!IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled()) &&
+            image) {
           if (lruCache_)
             [lruCache_ setObject:image forKey:sessionID];
           else
@@ -252,10 +254,8 @@ void ConvertAndSaveGreyImage(
   if (!img || !sessionID)
     return;
 
-  // The iPad tab switcher is currently using its own memory cache so the image
-  // is not stored in memory here if running on iPad.
-  // The same logic is used on image reads (code above).
-  if (!IsIPadIdiom()) {
+  // Cache on iPad is enabled only when the tab switcher is enabled.
+  if (!IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled()) {
     if (lruCache_)
       [lruCache_ setObject:img forKey:sessionID];
     else
@@ -387,7 +387,7 @@ void ConvertAndSaveGreyImage(
 }
 
 - (void)handleLowMemory {
-  DCHECK(!IsIPadIdiom());
+  DCHECK(!IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled());
   DCHECK_CURRENTLY_ON_WEB_THREAD(web::WebThread::UI);
   NSMutableDictionary* dictionary =
       [[NSMutableDictionary alloc] initWithCapacity:2];
@@ -410,14 +410,14 @@ void ConvertAndSaveGreyImage(
 }
 
 - (void)handleEnterBackground {
-  DCHECK(!IsIPadIdiom());
+  DCHECK(!IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled());
   DCHECK_CURRENTLY_ON_WEB_THREAD(web::WebThread::UI);
   [imageDictionary_ removeAllObjects];
   [lruCache_ removeAllObjects];
 }
 
 - (void)handleBecomeActive {
-  DCHECK(!IsIPadIdiom());
+  DCHECK(!IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled());
   DCHECK_CURRENTLY_ON_WEB_THREAD(web::WebThread::UI);
   for (NSString* sessionID in pinnedIDs_)
     [self retrieveImageForSessionID:sessionID callback:nil];

ios/chrome/browser/snapshots/snapshot_cache_unittest.mm

@@ -216,7 +216,7 @@ class SnapshotCacheTest : public PlatformTest {
 TEST_F(SnapshotCacheTest, Cache) {
   // Don't run on tablets because color snapshots are not cached so this test
   // can't compare the UIImage pointers directly.
-  if (IsIPadIdiom()) {
+  if (IsIPadIdiom() && !experimental_flags::IsTabSwitcherEnabled()) {
     return;
   }
 
@@ -368,13 +368,13 @@ TEST_F(SnapshotCacheTest, HandleLowMemory) {
   [set addObject:secondPinnedID];
   cache.pinnedIDs = set;
 
-  if (!IsIPadIdiom())
+  if (!IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled())
     [cache handleLowMemory];
 
   BOOL expectedValue = YES;
-  if (IsIPadIdiom()) {
+  if (IsIPadIdiom() && !experimental_flags::IsTabSwitcherEnabled())
     expectedValue = NO;
-  }
+
   EXPECT_EQ(expectedValue, [cache hasImageInMemory:firstPinnedID]);
   EXPECT_EQ(expectedValue, [cache hasImageInMemory:secondPinnedID]);
 
@@ -423,7 +423,7 @@ TEST_F(SnapshotCacheTest, CreateGreyCacheFromDisk) {
   // Remove color images from in-memory cache.
   SnapshotCache* cache = GetSnapshotCache();
 
-  if (!IsIPadIdiom())
+  if (!IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled())
     [cache handleLowMemory];
 
   // Request the creation of a grey image cache for all images.
@@ -465,7 +465,7 @@ TEST_F(SnapshotCacheTest, MostRecentGreyBlock) {
   LoadColorImagesIntoCache(kNumImages, true);
   // Make sure the color images are only on disk, to ensure the background
   // thread is slow enough to queue up the requests.
-  if (!IsIPadIdiom())
+  if (!IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled())
     [cache handleLowMemory];
 
   // Enable the grey image cache.
@@ -537,7 +537,7 @@ TEST_F(SnapshotCacheTest, SizeAndScalePreservation) {
   NSString* const kSession = @"foo";
   [cache setImage:image withSessionID:kSession];
   FlushRunLoops();  // ensure the file is written to disk.
-  if (!IsIPadIdiom())
+  if (!IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled())
     [cache handleLowMemory];
 
   // Retrive the image and have the callback verify the size and scale.
@@ -574,7 +574,7 @@ TEST_F(SnapshotCacheTest, DeleteRetinaImages) {
   NSString* const kSession = @"foo";
   [cache setImage:image withSessionID:kSession];
   FlushRunLoops();  // ensure the file is written to disk.
-  if (!IsIPadIdiom())
+  if (!IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled())
     [cache handleLowMemory];
 
   // Verify the file was writted with @2x in the file name.