Redraw only dirty area for accelerated 2D Canvas.

Source/platform/graphics/GraphicsLayer.h

 /*
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Intel Corporation. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 180 matching lines @@
     void setBackgroundFilters(const FilterOperations&);
 
     // Some GraphicsLayers paint only the foreground or the background content
     void setPaintingPhase(GraphicsLayerPaintingPhase);
 
     void setNeedsDisplay();
     // mark the given rect (in layer coords) as needing dispay. Never goes deep.
     void setNeedsDisplayInRect(const FloatRect&);
 
     void setContentsNeedsDisplay();
+    void setContentsNeedsDisplayInRect(const FloatRect&);
 
     // Set that the position/size of the contents (image or video).
     void setContentsRect(const IntRect&);
 
     // Return true if the animation is handled by the compositing system. If this returns
     // false, the animation will be run by AnimationController.
     // These methods handle both transitions and keyframe animations.
     bool addAnimation(PassOwnPtr<blink::WebAnimation>);
     void pauseAnimation(int animationId, double /*timeOffset*/);
     void removeAnimation(int animationId);
@@ skipping 156 matching lines @@
 };
 
 } // namespace WebCore
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void PLATFORM_EXPORT showGraphicsLayerTree(const WebCore::GraphicsLayer*);
 #endif
 
 #endif // GraphicsLayer_h