Redraw only dirty area for accelerated 2D Canvas.

Source/core/html/canvas/CanvasRenderingContext2D.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008 Dirk Schulze <krit@webkit.org>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  * Copyright (C) 2012, 2013 Intel Corporation. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
@@ skipping 1725 matching lines @@
         *dirtyRect = canvasRect;
 
     return true;
 }
 
 void CanvasRenderingContext2D::didDraw(const FloatRect& dirtyRect)
 {
     if (dirtyRect.isEmpty())
         return;
 
-    // If we are drawing to hardware and we have a composited layer, just call contentChanged().
-    if (isAccelerated()) {
-        RenderBox* renderBox = canvas()->renderBox();
-        if (renderBox && renderBox->hasAcceleratedCompositing()) {
-            renderBox->contentChanged(CanvasPixelsChanged);
-            canvas()->clearCopiedImage();
-            canvas()->notifyObserversCanvasChanged(dirtyRect);
-            return;
-        }
+    // If we are drawing to hardware and we have a composited layer, just invalidate layer.
+    if (isAccelerated() && platformLayer()) {
+        platformLayer()->invalidateRect(dirtyRect);
+        canvas()->clearCopiedImage();
+        canvas()->notifyObserversCanvasChanged(dirtyRect);
+        return;
     }
 
     canvas()->didDraw(dirtyRect);
 }
 
 GraphicsContext* CanvasRenderingContext2D::drawingContext() const
 {
     if (isContextLost())
         return 0;
     return canvas()->drawingContext();
@@ skipping 670 matching lines @@
 
 unsigned CanvasRenderingContext2D::hitRegionsCount() const
 {
     if (m_hitRegionManager)
         return m_hitRegionManager->getHitRegionsCount();
 
     return 0;
 }
 
 } // namespace WebCore