Implement "Save image as" for canvas (blink side).

public/web/WebView.h

 /*
  * Copyright (C) 2009, 2010, 2011, 2012 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 320 matching lines @@
 
     // Data exchange -------------------------------------------------------
 
     // Do a hit test at given point and return the HitTestResult.
     virtual WebHitTestResult hitTestResultAt(const WebPoint&) = 0;
 
     // Copy to the clipboard the image located at a particular point in the
     // WebView (if there is such an image)
     virtual void copyImageAt(const WebPoint&) = 0;
 
+    // Save as the image located at a particular point in the
+    // WebView (if there is such an image)
+    virtual void saveImageAt(const WebPoint&) = 0;
+
     // Notifies the WebView that a drag has terminated.
     virtual void dragSourceEndedAt(
         const WebPoint& clientPoint, const WebPoint& screenPoint,
         WebDragOperation operation) = 0;
 
     // Notfies the WebView that the system drag and drop operation has ended.
     virtual void dragSourceSystemDragEnded() = 0;
 
     // Callback methods when a drag-and-drop operation is trying to drop
     // something on the WebView.
@@ skipping 150 matching lines @@
 
     // Testing functionality for TestRunner ---------------------------------
 
 protected:
     ~WebView() {}
 };
 
 } // namespace blink
 
 #endif