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

content/public/browser/render_view_host.h

 // Copyright (c) 2012 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 CONTENT_PUBLIC_BROWSER_RENDER_VIEW_HOST_H_
 #define CONTENT_PUBLIC_BROWSER_RENDER_VIEW_HOST_H_
 
 #include <list>
 
 #include "base/callback_forward.h"
@@ skipping 73 matching lines @@
 
   // Causes the renderer to close the current page, including running its
   // onunload event handler.  A ClosePage_ACK message will be sent to the
   // ResourceDispatcherHost when it is finished.
   virtual void ClosePage() = 0;
 
   // Copies the image at location x, y to the clipboard (if there indeed is an
   // image at that location).
   virtual void CopyImageAt(int x, int y) = 0;
 
+  // Saves the image at location x, y to the disk (if there indeed is an
+  // image at that location).
+  virtual void SaveImageAt(int x, int y) = 0;
+
   // Notifies the listener that a directory enumeration is complete.
   virtual void DirectoryEnumerationFinished(
       int request_id,
       const std::vector<base::FilePath>& files) = 0;
 
   // Tells the renderer not to add scrollbars with height and width below a
   // threshold.
   virtual void DisableScrollbarsForThreshold(const gfx::Size& size) = 0;
 
   // Notifies the renderer that a a drag operation that it started has ended,
@@ skipping 115 matching lines @@
 
  private:
   // This interface should only be implemented inside content.
   friend class RenderViewHostImpl;
   RenderViewHost() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_RENDER_VIEW_HOST_H_