cc: Clear checker-image tracking on navigation and visibility changes.

cc/tiles/checker_image_tracker.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_TILES_CHECKER_IMAGE_TRACKER_H_
 #define CC_TILES_CHECKER_IMAGE_TRACKER_H_
 
 #include <unordered_map>
 #include <vector>
 
@@ skipping 29 matching lines @@
   // Returns true if the decode for |image| will be deferred to the image decode
   // service and it should be be skipped during raster.
   bool ShouldCheckerImage(const sk_sp<const SkImage>& image, WhichTree tree);
 
   using ImageDecodeQueue = std::vector<sk_sp<const SkImage>>;
   void ScheduleImageDecodeQueue(ImageDecodeQueue image_decode_queue);
 
   // Returns the set of images to invalidate on the sync tree.
   const ImageIdFlatSet& TakeImagesToInvalidateOnSyncTree();
 
+  // Called when the sync tree is activated. Each call to
+  // TakeImagesToInvalidateOnSyncTree() must be followed by this when the
+  // invalidated sync tree is activated.
   void DidActivateSyncTree();
 
+  // Called to reset the tracker state on navigation or when going invisible.
+  void ClearTracker();
+
  private:
   enum class DecodePolicy {
     // The image can be decoded asynchronously from raster. When set, the image
     // is always skipped during rasterization of content that includes this
     // image until it has been decoded using the decode service.
     ASYNC,
     // The image has been decoded asynchronously once and should now be
     // synchronously rasterized with the content.
     SYNC_DECODED_ONCE,
     // The image has been permanently vetoed from being decoded async.
     SYNC_PERMANENT,
   };
 
+  class ScopedDecodeHolder {

[vmpstr, 2017/05/09 22:06:21]

ScopedDecodeUnlocker maybe? Can you also drop a class comment here to explain
what it does

[Khushal, 2017/05/10 22:47:09]

Done.

+   public:
+    ScopedDecodeHolder(ImageController* controller,
+                       ImageController::ImageDecodeRequestId request_id)
+        : controller_(controller), request_id_(request_id) {}
+    ~ScopedDecodeHolder() { controller_->UnlockImageDecode(request_id_); }
+
+   private:
+    ImageController* controller_;
+    ImageController::ImageDecodeRequestId request_id_;
+
+    DISALLOW_COPY_AND_ASSIGN(ScopedDecodeHolder);
+  };
+
   void DidFinishImageDecode(ImageId image_id,
                             ImageController::ImageDecodeRequestId request_id,
                             ImageController::ImageDecodeResult result);
 
   // Called when the next request in the |image_decode_queue_| should be
   // scheduled with the image decode service.
   void ScheduleNextImageDecode();
 
   ImageController* image_controller_;
   CheckerImageTrackerClient* client_;
   const bool enable_checker_imaging_;
 
   // A set of images which have been decoded and are pending invalidation for
   // raster on the checkered tiles.
   ImageIdFlatSet images_pending_invalidation_;
 
   // A set of images which were invalidated on the current sync tree.
   ImageIdFlatSet invalidated_images_on_current_sync_tree_;
 
   // The queue of images pending decode. We maintain a queue to ensure that the
   // order in which images are decoded is aligned with the priority of the tiles
   // dependent on these images.
   ImageDecodeQueue image_decode_queue_;
 
   // The currently outstanding image decode that has been scheduled with the
   // decode service. There can be only one outstanding decode at a time.
   sk_sp<const SkImage> outstanding_image_decode_;
 
   // A map of ImageId to its DecodePolicy.
-  // TODO(khushalsagar): Limit the size of this set.
-  // TODO(khushalsagar): Plumb navigation changes here to reset this. See
-  // crbug.com/693228.
   std::unordered_map<ImageId, DecodePolicy> image_async_decode_state_;
 
   // A map of image id to image decode request id for images to be unlocked.
-  std::unordered_map<ImageId, ImageController::ImageDecodeRequestId>
-      image_id_to_decode_request_id_;
+  std::unordered_map<ImageId, std::unique_ptr<ScopedDecodeHolder>>
+      image_id_to_decode_;
 
   base::WeakPtrFactory<CheckerImageTracker> weak_factory_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TILES_CHECKER_IMAGE_TRACKER_H_