Use SkImage as a backing store for copying 2d Contexts to ImageBitmaps.

Source/core/page/ImageBitmap.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ImageBitmap_h
 #define ImageBitmap_h
 
 #include "bindings/v8/ScriptWrappable.h"
 #include "core/html/HTMLImageElement.h"
 #include "core/platform/graphics/Image.h"
@@ skipping 15 matching lines @@
     static PassRefPtr<ImageBitmap> create(HTMLVideoElement*, const IntRect&);
     static PassRefPtr<ImageBitmap> create(HTMLCanvasElement*, const IntRect&);
     static PassRefPtr<ImageBitmap> create(ImageData*, const IntRect&);
     static PassRefPtr<ImageBitmap> create(ImageBitmap*, const IntRect&);
 
     PassRefPtr<Image> bitmapImage() const;
     PassRefPtr<HTMLImageElement> imageElement() const { return m_imageElement; }
 
     IntRect bitmapRect() const { return m_bitmapRect; }
     IntPoint bitmapOffset() const { return m_bitmapOffset; }
+    bool derivedFromCanvas() const { return m_derivedFromCanvas; }
 
     int width() const { return m_cropRect.width(); }
     int height() const { return m_cropRect.height(); }
     IntSize size() const { return m_cropRect.size(); }
 
     virtual ~ImageBitmap();
 
 private:
     ImageBitmap(HTMLImageElement*, const IntRect&);
     ImageBitmap(HTMLVideoElement*, const IntRect&);
     ImageBitmap(HTMLCanvasElement*, const IntRect&);
     ImageBitmap(ImageData*, const IntRect&);
     ImageBitmap(ImageBitmap*, const IntRect&);
 
     // ImageLoaderClient
     virtual void notifyImageSourceChanged();
     virtual bool requestsHighLiveResourceCachePriority() { return true; }
 
     // ImageBitmaps constructed from HTMLImageElements hold a reference to the HTMLImageElement until
     // the image source changes.
     RefPtr<HTMLImageElement> m_imageElement;
     RefPtr<Image> m_bitmap;
     OwnPtr<ImageBuffer> m_buffer;
 
     IntRect m_bitmapRect; // The rect where the underlying Image should be placed in reference to the ImageBitmap.
     IntRect m_cropRect;
 
     // The offset by which the desired Image is stored internally.
-    // ImageBitmaps constructed from HTMLImageElements reference the entire CachedImage and may have a non-zero bitmap offset.
-    // ImageBitmaps not constructed from HTMLImageElements always pre-crop and store the image at (0, 0).
+    // ImageBitmaps constructed from image elements or canvases reference the entire CachedImage and may have a non-zero bitmap offset.
+    // Otherwise, ImageBitmaps pre-crop and store the image at (0, 0).
     IntPoint m_bitmapOffset;
 
+    unsigned m_derivedFromCanvas : 1;
 };
 
 } // namespace WebCore
 
 #endif // ImageBitmap_h