[ios] Use properties over ivars in SnapshotGenerator

This CL fixes a retain cycle that was caused by using an ivar in an
asynchronous block. The block retains self when an ivar is used.
This CL also more broadly replaces ivars with properties in the same
file.

Bug: 918032
Change-Id: I26c867931ad96574f19420f58465e2d14c43ce43
Reviewed-on: https://chromium-review.googlesource.com/c/1393015Reviewed-by: Eric Noyau <noyau@chromium.org>
Reviewed-by: edchin <edchin@chromium.org>
Commit-Queue: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619922}

ios/chrome/browser/snapshots/snapshot_generator.mm

@@ -48,12 +48,16 @@ BOOL ViewHierarchyContainsWKWebView(UIView* view) {
 // Property providing access to the snapshot's cache. May be nil.
 @property(nonatomic, readonly) SnapshotCache* snapshotCache;
 
+// The unique ID for the web state.
+@property(nonatomic, copy) NSString* sessionID;
+
+// The associated web state.
+@property(nonatomic, assign) web::WebState* webState;
+
 @end
 
 @implementation SnapshotGenerator {
   std::unique_ptr<web::WebStateObserver> _webStateObserver;
-  NSString* _snapshotSessionId;
-  web::WebState* _webState;
 }
 
 - (instancetype)initWithWebState:(web::WebState*)webState
@@ -62,7 +66,7 @@ BOOL ViewHierarchyContainsWKWebView(UIView* view) {
     DCHECK(webState);
     DCHECK(snapshotSessionId);
     _webState = webState;
-    _snapshotSessionId = snapshotSessionId;
+    _sessionID = snapshotSessionId;
 
     _webStateObserver = std::make_unique<web::WebStateObserverBridge>(self);
     _webState->AddObserver(_webStateObserver.get());
@@ -81,7 +85,7 @@ BOOL ViewHierarchyContainsWKWebView(UIView* view) {
 - (void)retrieveSnapshot:(void (^)(UIImage*))callback {
   DCHECK(callback);
   if (self.snapshotCache) {
-    [self.snapshotCache retrieveImageForSessionID:_snapshotSessionId
+    [self.snapshotCache retrieveImageForSessionID:self.sessionID
                                          callback:callback];
   } else {
     callback(nil);
@@ -103,7 +107,7 @@ BOOL ViewHierarchyContainsWKWebView(UIView* view) {
 
   SnapshotCache* snapshotCache = self.snapshotCache;
   if (snapshotCache) {
-    [snapshotCache retrieveGreyImageForSessionID:_snapshotSessionId
+    [snapshotCache retrieveGreyImageForSessionID:self.sessionID
                                         callback:wrappedCallback];
   } else {
     wrappedCallback(nil);
@@ -113,17 +117,18 @@ BOOL ViewHierarchyContainsWKWebView(UIView* view) {
 - (UIImage*)updateSnapshot {
   UIImage* snapshot = [self generateSnapshotWithOverlays:YES];
   if (snapshot) {
-    [self.snapshotCache setImage:snapshot withSessionID:_snapshotSessionId];
+    [self.snapshotCache setImage:snapshot withSessionID:self.sessionID];
   }
   return snapshot;
 }
 
 - (void)updateWebViewSnapshotWithCompletion:(void (^)(UIImage*))completion {
-  DCHECK(_webState);
+  DCHECK(self.webState);
   UIView* snapshotView = [self.delegate snapshotGenerator:self
-                                      baseViewForWebState:_webState];
-  CGRect snapshotFrame = [_webState->GetView() convertRect:[self snapshotFrame]
-                                                  fromView:snapshotView];
+                                      baseViewForWebState:self.webState];
+  CGRect snapshotFrame =
+      [self.webState->GetView() convertRect:[self snapshotFrame]
+                                   fromView:snapshotView];
   if (CGRectIsEmpty(snapshotFrame)) {
     if (completion) {
       base::PostTaskWithTraits(FROM_HERE, {web::WebThread::UI},
@@ -138,36 +143,19 @@ BOOL ViewHierarchyContainsWKWebView(UIView* view) {
       << ": snapshotFrame.size.width=" << size.width;
   DCHECK(std::isnormal(size.height) && (size.height > 0))
       << ": snapshotFrame.size.height=" << size.height;
-  NSArray<SnapshotOverlay*>* overlays = [_delegate snapshotGenerator:self
-                                         snapshotOverlaysForWebState:_webState];
+  NSArray<SnapshotOverlay*>* overlays =
+      [self.delegate snapshotGenerator:self
+           snapshotOverlaysForWebState:self.webState];
 
-  [_delegate snapshotGenerator:self willUpdateSnapshotForWebState:_webState];
+  [self.delegate snapshotGenerator:self
+      willUpdateSnapshotForWebState:self.webState];
   __weak SnapshotGenerator* weakSelf = self;
-  _webState->TakeSnapshot(
+  self.webState->TakeSnapshot(
       snapshotFrame, base::BindOnce(^(const gfx::Image& image) {
-        SnapshotGenerator* strongSelf = weakSelf;
-        if (!strongSelf || !_webState)
-          return;
-        UIImage* snapshot = nil;
-        if (!image.IsEmpty()) {
-          snapshot = image.ToUIImage();
-          if (overlays.count > 0) {
-            snapshot = [strongSelf snapshotWithOverlays:overlays
-                                               snapshot:snapshot
-                                                  frame:snapshotFrame];
-          }
-        }
-        if (snapshot) {
-          [strongSelf.snapshotCache setImage:snapshot
-                               withSessionID:_snapshotSessionId];
-        } else {
-          // Remove any stale snapshot since the snapshot failed.
-          [strongSelf.snapshotCache
-              removeImageWithSessionID:_snapshotSessionId];
-        }
-        [_delegate snapshotGenerator:self
-            didUpdateSnapshotForWebState:_webState
-                               withImage:snapshot];
+        UIImage* snapshot = [weakSelf snapshotWithOverlays:overlays
+                                                     image:image
+                                                     frame:snapshotFrame];
+        [weakSelf updateSnapshotCacheWithImage:snapshot];
         if (completion)
           completion(snapshot);
       }));
@@ -179,24 +167,25 @@ BOOL ViewHierarchyContainsWKWebView(UIView* view) {
     return nil;
 
   NSArray<SnapshotOverlay*>* overlays =
-      shouldAddOverlay ? [_delegate snapshotGenerator:self
-                             snapshotOverlaysForWebState:_webState]
+      shouldAddOverlay ? [self.delegate snapshotGenerator:self
+                              snapshotOverlaysForWebState:self.webState]
                        : nil;
 
-  [_delegate snapshotGenerator:self willUpdateSnapshotForWebState:_webState];
-  UIView* view = [_delegate snapshotGenerator:self
-                          baseViewForWebState:_webState];
+  [self.delegate snapshotGenerator:self
+      willUpdateSnapshotForWebState:self.webState];
+  UIView* view = [self.delegate snapshotGenerator:self
+                              baseViewForWebState:self.webState];
   UIImage* snapshot = [self generateSnapshotForView:view
                                            withRect:frame
                                            overlays:overlays];
-  [_delegate snapshotGenerator:self
-      didUpdateSnapshotForWebState:_webState
+  [self.delegate snapshotGenerator:self
+      didUpdateSnapshotForWebState:self.webState
                          withImage:snapshot];
   return snapshot;
 }
 
 - (void)removeSnapshot {
-  [self.snapshotCache removeImageWithSessionID:_snapshotSessionId];
+  [self.snapshotCache removeImageWithSessionID:self.sessionID];
 }
 
 #pragma mark - Private methods
@@ -206,19 +195,19 @@ BOOL ViewHierarchyContainsWKWebView(UIView* view) {
 - (CGRect)snapshotFrame {
   // Do not generate a snapshot if web usage is disabled (as the WebState's
   // view is blank in that case).
-  if (!_webState->IsWebUsageEnabled())
+  if (!self.webState->IsWebUsageEnabled())
     return CGRectZero;
 
   // Do not generate a snapshot if the delegate says the WebState view is
   // not ready (this generally mean a placeholder is displayed).
-  if (_delegate && ![_delegate snapshotGenerator:self
-                       canTakeSnapshotForWebState:_webState])
+  if (self.delegate && ![self.delegate snapshotGenerator:self
+                              canTakeSnapshotForWebState:self.webState])
     return CGRectZero;
 
-  UIView* view = [_delegate snapshotGenerator:self
-                          baseViewForWebState:_webState];
-  UIEdgeInsets headerInsets = [_delegate snapshotGenerator:self
-                             snapshotEdgeInsetsForWebState:_webState];
+  UIView* view = [self.delegate snapshotGenerator:self
+                              baseViewForWebState:self.webState];
+  UIEdgeInsets headerInsets = [self.delegate snapshotGenerator:self
+                                 snapshotEdgeInsetsForWebState:self.webState];
   return UIEdgeInsetsInsetRect(view.bounds, headerInsets);
 }
 
@@ -286,11 +275,15 @@ BOOL ViewHierarchyContainsWKWebView(UIView* view) {
   return image;
 }
 
-// Returns an image of the |snapshot| overlaid with |overlays| with the given
+// Returns an image of the |image| overlaid with |overlays| with the given
 // |frame|.
 - (UIImage*)snapshotWithOverlays:(NSArray<SnapshotOverlay*>*)overlays
-                        snapshot:(UIImage*)snapshot
+                           image:(const gfx::Image&)image
                            frame:(CGRect)frame {
+  if (image.IsEmpty())
+    return nil;
+  if (overlays.count == 0)
+    return image.ToUIImage();
   CGSize size = frame.size;
   DCHECK(std::isnormal(size.width) && (size.width > 0))
       << ": size.width=" << size.width;
@@ -302,7 +295,7 @@ BOOL ViewHierarchyContainsWKWebView(UIView* view) {
   CGContext* context = UIGraphicsGetCurrentContext();
   DCHECK(context);
   CGContextSaveGState(context);
-  [snapshot drawAtPoint:CGPointZero];
+  [image.ToUIImage() drawAtPoint:CGPointZero];
   for (SnapshotOverlay* overlay in overlays) {
     // Render the overlay view at the desired offset. It is achieved
     // by shifting origin of context because view frame is ignored when
@@ -327,11 +320,25 @@ BOOL ViewHierarchyContainsWKWebView(UIView* view) {
   return snapshotWithOverlays;
 }
 
+// Updates the snapshot cache with |snapshot|.
+- (void)updateSnapshotCacheWithImage:(UIImage*)snapshot {
+  if (snapshot) {
+    [self.snapshotCache setImage:snapshot withSessionID:self.sessionID];
+  } else {
+    // Remove any stale snapshot since the snapshot failed.
+    [self.snapshotCache removeImageWithSessionID:self.sessionID];
+  }
+  [self.delegate snapshotGenerator:self
+      didUpdateSnapshotForWebState:self.webState
+                         withImage:snapshot];
+}
+
 #pragma mark - Properties
 
 - (SnapshotCache*)snapshotCache {
   return SnapshotCacheFactory::GetForBrowserState(
-      ios::ChromeBrowserState::FromBrowserState(_webState->GetBrowserState()));
+      ios::ChromeBrowserState::FromBrowserState(
+          self.webState->GetBrowserState()));
 }
 
 #pragma mark - CRWWebStateObserver