[AppRemoting] Implement ConnectionDroppedDialog.

remoting/webapp/app_remoting/js/context_menu_chrome.js

 // 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.
 
 /**
  * @fileoverview
  * remoting.ContextMenuAdapter implementation backed by chrome.contextMenus.
  */
 
 'use strict';
 
 /** @suppress {duplicate} */
 var remoting = remoting || {};
 
 /**
  * @constructor
  * @implements {remoting.ContextMenuAdapter}
  */
 remoting.ContextMenuChrome = function() {};
 
-remoting.ContextMenuChrome.prototype.dispose = function() {};
+remoting.ContextMenuChrome.prototype.dispose = function() {
+  chrome.contextMenus.removeAll();
+};
 
 /**
  * @param {string} id An identifier for the menu entry.
  * @param {string} title The text to display in the menu.
  * @param {boolean} isCheckable True if the state of this menu entry should
  *     have a check-box and manage its toggle state automatically.
  * @param {string=} opt_parentId The id of the parent menu item for submenus.
  */
 remoting.ContextMenuChrome.prototype.create = function(
     id, title, isCheckable, opt_parentId) {
@@ skipping 52 matching lines @@
 };
 
 /**
  * @param {*} message
  * @param {Window} backgroundPage
  */
 remoting.ContextMenuChrome.prototype.postMessage_ = function(
     message, backgroundPage) {
   backgroundPage.postMessage(message, '*');
 };