cc: Move pre-decodes to background worker.

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 15 matching lines @@
 // CheckerImageTracker is used to track the set of images in a frame which are
 // decoded asynchronously, using the ImageDecodeService, from the rasterization
 // of tiles which depend on them. Once decoded, these images are stored for
 // invalidation on the next sync tree. TakeImagesToInvalidateOnSyncTree will
 // return this set and maintain a copy to keeps these images locked until the
 // sync tree is activated.
 // Note: It is illegal to call TakeImagesToInvalidateOnSyncTree for the next
 // sync tree until the previous tree is activated.
 class CC_EXPORT CheckerImageTracker {
  public:
+  enum class DecodeType : uint16_t {
+    // Highest priority. Used to disable scheduling any decode work.
+    kNone,

[vmpstr, 2017/06/20 18:41:01]

This is an awkward name. Just from looking at this, I wouldn't know when to say
DecodeType::kNone. How is this used? Is there a more descriptive name we can use
here?

[Khushal, 2017/06/21 23:45:28]

I just made it all internal so we wouldn't need to expose something in this enum
to let the caller disable all decodes.

+    // Priority for images on tiles being rasterized (visible or pre-paint).
+    kRaster,
+    // Lowest priority for images on tiles in pre-decode region. These are tiles
+    // which are beyond the pre-paint region, but have their images decoded.
+    kPreDecode
+  };
+
+  struct ImageDecodeRequest {
+    ImageDecodeRequest(PaintImage paint_image, DecodeType type);
+    PaintImage paint_image;
+    DecodeType type;
+  };
+
   CheckerImageTracker(ImageController* image_controller,
                       CheckerImageTrackerClient* client,
                       bool enable_checker_imaging);
   ~CheckerImageTracker();
 
   // 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 DrawImage& image, WhichTree tree);
 
-  using ImageDecodeQueue = std::vector<PaintImage>;
+  // Provides a prioritized queue of images to decode.
+  using ImageDecodeQueue = std::vector<ImageDecodeRequest>;
   void ScheduleImageDecodeQueue(ImageDecodeQueue image_decode_queue);
 
+  // The max decode priority type that is allowed to run.

[vmpstr, 2017/06/20 18:41:01]

Can you use the word "max" or "limit" in the function name to make it clear that
everything specified and below can run?

[Khushal, 2017/06/21 03:35:57]

Done.

+  void SetCanScheduleDecodeType(DecodeType decode_type);
+
   // Returns the set of images to invalidate on the sync tree.
   const PaintImageIdFlatSet& 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. This will release all
   // cached images. Setting |can_clear_decode_policy_tracking| will also result
@@ skipping 65 matching lines @@
   PaintImageIdFlatSet images_pending_invalidation_;
 
   // A set of images which were invalidated on the current sync tree.
   PaintImageIdFlatSet 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 max decode type that is allowed to run.
+  DecodeType decode_type_allowed_;
+
   // The currently outstanding image decode that has been scheduled with the
   // decode service. There can be only one outstanding decode at a time.
   base::Optional<PaintImage> outstanding_image_decode_;
 
   // A map of ImageId to its DecodePolicy.
   std::unordered_map<PaintImage::Id, DecodeState> image_async_decode_state_;
 
   // A map of image id to image decode request id for images to be unlocked.
   std::unordered_map<PaintImage::Id, std::unique_ptr<ScopedDecodeHolder>>
       image_id_to_decode_;
 
   base::WeakPtrFactory<CheckerImageTracker> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(CheckerImageTracker);
 };
 
 }  // namespace cc
 
 #endif  // CC_TILES_CHECKER_IMAGE_TRACKER_H_