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

Source/web/WebViewImpl.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 190 matching lines @@
         const WebSize& maxSize) OVERRIDE;
     virtual void disableAutoResizeMode() OVERRIDE;
     virtual void performMediaPlayerAction(
         const WebMediaPlayerAction& action,
         const WebPoint& location) OVERRIDE;
     virtual void performPluginAction(
         const WebPluginAction&,
         const WebPoint&) OVERRIDE;
     virtual WebHitTestResult hitTestResultAt(const WebPoint&) OVERRIDE;
     virtual void copyImageAt(const WebPoint&) OVERRIDE;
+    virtual void saveImageAt(const WebPoint&) OVERRIDE;
     virtual void dragSourceEndedAt(
         const WebPoint& clientPoint,
         const WebPoint& screenPoint,
         WebDragOperation) OVERRIDE;
     virtual void dragSourceSystemDragEnded() OVERRIDE;
     virtual WebDragOperation dragTargetDragEnter(
         const WebDragData&,
         const WebPoint& clientPoint,
         const WebPoint& screenPoint,
         WebDragOperationsMask operationsAllowed,
@@ skipping 505 matching lines @@
     bool m_userGestureObserved;
 };
 
 // We have no ways to check if the specified WebView is an instance of
 // WebViewImpl because WebViewImpl is the only implementation of WebView.
 DEFINE_TYPE_CASTS(WebViewImpl, WebView, webView, true, true);
 
 } // namespace blink
 
 #endif