Free temporary GPU and memory resources held by inactive or hidden 2D canvases

Source/platform/graphics/ImageBufferSurface.h

 /*
  * Copyright (c) 2013, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 47 matching lines @@
     virtual const SkBitmap& bitmap() const;
     virtual void willUse() { } // Called by ImageBuffer before reading or writing to the surface.
     virtual bool isValid() const = 0;
     virtual blink::WebLayer* layer() const { return 0; };
     virtual bool isAccelerated() const { return false; }
     virtual Platform3DObject getBackingTexture() const { return 0; }
     virtual bool cachedBitmapEnabled() const { return false; }
     virtual const SkBitmap& cachedBitmap() const;
     virtual void invalidateCachedBitmap() { }
     virtual void updateCachedBitmapIfNeeded() { }
+    virtual void setIsHidden(bool) { }
 
     OpacityMode opacityMode() const { return m_opacityMode; }
     const IntSize& size() const { return m_size; }
 
 protected:
     void clear();
 
     ImageBufferSurface(const IntSize& size, OpacityMode opacityMode)
         : m_opacityMode(opacityMode)
         , m_size(size)
-    { }
+    {
+        setIsHidden(false);
+    }
 
 private:
     OpacityMode m_opacityMode;
     IntSize m_size;
 };
 
 } // namespace WebCore
 
 #endif