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

chrome/browser/renderer_context_menu/render_view_context_menu.h

 // Copyright 2014 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 CHROME_BROWSER_RENDERER_CONTEXT_MENU_RENDER_VIEW_CONTEXT_MENU_H_
 #define CHROME_BROWSER_RENDERER_CONTEXT_MENU_RENDER_VIEW_CONTEXT_MENU_H_
 
 #include <map>
 #include <string>
 
@@ skipping 193 matching lines @@
 
   // Gets the extension (if any) associated with the WebContents that we're in.
   const extensions::Extension* GetExtension() const;
   bool AppendCustomItems();
 
   void AppendDeveloperItems();
   void AppendDevtoolsForUnpackedExtensions();
   void AppendLinkItems();
   void AppendImageItems();
   void AppendAudioItems();
+  void AppendCanvasItems();
   void AppendVideoItems();
   void AppendMediaItems();
   void AppendPluginItems();
   void AppendPageItems();
   void AppendFrameItems();
   void AppendCopyItem();
   void AppendPrintItem();
   void AppendEditableItems();
   void AppendSearchProvider();
   void AppendAllExtensionItems();
@@ skipping 62 matching lines @@
   // Whether a command has been executed. Used to track whether menu observers
   // should be notified of menu closing without execution.
   bool command_executed_;
 
   scoped_ptr<ContextMenuContentType> content_type_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderViewContextMenu);
 };
 
 #endif  // CHROME_BROWSER_RENDERER_CONTEXT_MENU_RENDER_VIEW_CONTEXT_MENU_H_