Redraw only dirty area for accelerated 2D Canvas.

Source/core/rendering/RenderBoxModelObject.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2006, 2007, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 28 matching lines @@
 enum BackgroundBleedAvoidance {
     BackgroundBleedNone,
     BackgroundBleedShrinkBackground,
     BackgroundBleedClipBackground,
     BackgroundBleedBackgroundOverBorder
 };
 
 enum ContentChangeType {
     ImageChanged,
     CanvasChanged,
-    CanvasPixelsChanged,
     CanvasContextChanged
 };
 
 class RenderTextFragment;
 class StickyPositionViewportConstraints;
 
 // This class is the base for all objects that adhere to the CSS box model as described
 // at http://www.w3.org/TR/CSS21/box.html
 
 class RenderBoxModelObject : public RenderLayerModelObject {
@@ skipping 270 matching lines @@
     void drawBoxSideFromPath(GraphicsContext*, const LayoutRect&, const Path&, const class BorderEdge[],
                             float thickness, float drawThickness, BoxSide, const RenderStyle*,
                             Color, EBorderStyle, BackgroundBleedAvoidance, bool includeLogicalLeftEdge, bool includeLogicalRightEdge);
 };
 
 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderBoxModelObject, isBoxModelObject());
 
 } // namespace WebCore
 
 #endif // RenderBoxModelObject_h