Fix imageSourceURL() for WebGL elements.

Source/platform/graphics/gpu/DrawingBuffer.h

 /*
  * Copyright (c) 2010, 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 140 matching lines @@
     // Returns the actual context attributes for this drawing buffer which may differ from the
     // requested context attributes due to implementation limits.
     blink::WebGraphicsContext3D::Attributes getActualAttributes() const { return m_actualAttributes; }
 
     // WebExternalTextureLayerClient implementation.
     virtual bool prepareMailbox(blink::WebExternalTextureMailbox*, blink::WebExternalBitmap*) OVERRIDE;
     virtual void mailboxReleased(const blink::WebExternalTextureMailbox&) OVERRIDE;
 
     // Destroys the TEXTURE_2D binding for the owned context
     bool copyToPlatformTexture(blink::WebGraphicsContext3D*, Platform3DObject texture, GLenum internalFormat,
-        GLenum destType, GLint level, bool premultiplyAlpha, bool flipY);
+        GLenum destType, GLint level, bool premultiplyAlpha, bool flipY, bool fromFrontBuffer = false);
 
     void setPackAlignment(GLint param);
 
     void paintRenderingResultsToCanvas(ImageBuffer*);
     PassRefPtr<Uint8ClampedArray> paintRenderingResultsToImageData(int&, int&);
 
 protected: // For unittests
     DrawingBuffer(
         PassOwnPtr<blink::WebGraphicsContext3D>,
         PassOwnPtr<Extensions3DUtil>,
@@ skipping 124 matching lines @@
     // used to resize the Canvas.
     SkBitmap m_resizingBitmap;
 
     // Used to flip a bitmap vertically.
     Vector<uint8_t> m_scanline;
 };
 
 } // namespace WebCore
 
 #endif // DrawingBuffer_h