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

Source/web/ContextMenuClientImpl.cpp

 /*
  * Copyright (C) 2009, 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 197 matching lines @@
     if (toLocalFrame(m_webView->focusedWebCoreFrame())->editor().canDelete())
         data.editFlags |= WebContextMenuData::CanDelete;
     // We can always select all...
     data.editFlags |= WebContextMenuData::CanSelectAll;
     data.editFlags |= WebContextMenuData::CanTranslate;
 
     // Links, Images, Media tags, and Image/Media-Links take preference over
     // all else.
     data.linkURL = r.absoluteLinkURL();
 
-    if (!r.absoluteImageURL().isEmpty()) {
+    if (isHTMLCanvasElement(r.innerNonSharedNode())) {
+        data.mediaType = WebContextMenuData::MediaTypeCanvas;
+    } else if (!r.absoluteImageURL().isEmpty()) {
         data.srcURL = r.absoluteImageURL();
         data.mediaType = WebContextMenuData::MediaTypeImage;
         data.mediaFlags |= WebContextMenuData::MediaCanPrint;
     } else if (!r.absoluteMediaURL().isEmpty()) {
         data.srcURL = r.absoluteMediaURL();
 
         // We know that if absoluteMediaURL() is not empty, then this
         // is a media element.
         HTMLMediaElement* mediaElement = toHTMLMediaElement(r.innerNonSharedNode());
         if (isHTMLVideoElement(*mediaElement))
@@ skipping 191 matching lines @@
         outputItems[i] = subItems[i];
     subMenuItems.swap(outputItems);
 }
 
 void ContextMenuClientImpl::populateCustomMenuItems(const WebCore::ContextMenu* defaultMenu, WebContextMenuData* data)
 {
     populateSubMenuItems(defaultMenu->items(), data->customItems);
 }
 
 } // namespace blink