Adding cache for security origin validations in 2D/WebGL canvases

Source/core/html/canvas/CanvasImageSource.h

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Computer, Inc.  All rights reserved.
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 48 matching lines @@
     virtual bool wouldTaintOrigin(SecurityOrigin* destinationSecurityOrigin) const = 0;
 
     virtual bool isVideoElement() const { return false; }
 
     // Adjusts the source and destination rectangles for cases where the actual
     // source image is a subregion of the image returned by getSourceImageForCanvas.
     virtual void adjustDrawRects(FloatRect* srcRect, FloatRect* dstRect) const { }
 
     virtual FloatSize sourceSize() const = 0;
     virtual FloatSize defaultDestinationSize() const { return sourceSize(); }
+    virtual const KURL& sourceURL() const { return blankURL(); }
 
 protected:
     virtual ~CanvasImageSource() { }
 };
 
 } // namespace WebCore
 
 #endif