Do not show menu items added by extensions inside <webview>.

chrome/browser/tab_contents/render_view_context_menu.cc

 // Copyright 2013 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.
 
 #include "chrome/browser/tab_contents/render_view_context_menu.h"
 
 #include <algorithm>
 #include <set>
 #include <utility>
 
@@ skipping 634 matching lines @@
     AppendEditableItems();
   else if (has_selection)
     AppendCopyItem();
 
   if (!is_guest_ && has_selection) {
     AppendSearchProvider();
     if (!IsDevToolsURL(params_.page_url))
       AppendPrintItem();
   }
 
-  if (!IsDevToolsURL(params_.page_url))
+  if (!IsDevToolsURL(params_.page_url) && !is_guest_)
     AppendAllExtensionItems();
 
   AppendDeveloperItems();
 
   if (!is_guest_) {
 #if defined(ENABLE_FULL_PRINTING)
     if (!print_preview_menu_observer_.get()) {
       print_preview_menu_observer_.reset(
           new PrintPreviewContextMenuObserver(source_web_contents_));
     }
@@ skipping 1443 matching lines @@
   source_web_contents_->GetRenderViewHost()->
       ExecuteMediaPlayerActionAtLocation(location, action);
 }
 
 void RenderViewContextMenu::PluginActionAt(
     const gfx::Point& location,
     const WebPluginAction& action) {
   source_web_contents_->GetRenderViewHost()->
       ExecutePluginActionAtLocation(location, action);
 }