cc: Move pre-decodes to background worker.

cc/tiles/checker_image_tracker.h

Index: cc/tiles/checker_image_tracker.h
diff --git a/cc/tiles/checker_image_tracker.h b/cc/tiles/checker_image_tracker.h
index 335050c6b9df5ec861be30f2f6b58f852bbebf07..a5b730845b06644b2333a11488a71a713d27aaed 100644
--- a/cc/tiles/checker_image_tracker.h
+++ b/cc/tiles/checker_image_tracker.h
@@ -33,6 +33,14 @@ class CC_EXPORT CheckerImageTrackerClient {
 // sync tree until the previous tree is activated.
 class CC_EXPORT CheckerImageTracker {
  public:
+  enum class DecodeType { kRaster, kPreDecode };

[vmpstr, 2017/06/12 21:45:30]

Comment please

[Khushal, 2017/06/14 00:29:19]

Done.

+
+  struct ImageDecodeRequest {
+    ImageDecodeRequest(PaintImage paint_image, DecodeType type);
+    PaintImage paint_image;
+    DecodeType type;
+  };
+
   CheckerImageTracker(ImageController* image_controller,
                       CheckerImageTrackerClient* client,
                       bool enable_checker_imaging);
@@ -42,9 +50,13 @@ class CC_EXPORT CheckerImageTracker {
   // 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);
 
+  // Sets whether decode work should be scheduled for pre-decode tiles.
+  void SetCanSchedulePredecodeImages(bool can_schedule_predecode_images);
+
   // Returns the set of images to invalidate on the sync tree.
   const PaintImageIdFlatSet& TakeImagesToInvalidateOnSyncTree();
 
@@ -130,6 +142,9 @@ class CC_EXPORT CheckerImageTracker {
   // dependent on these images.
   ImageDecodeQueue image_decode_queue_;
 
+  // Whether we can schedule decodes for pre-decoded images.
+  bool can_schedule_predecode_images_ = false;
+
   // 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_;