Add paper-menu-button and its dependencies to third_party/polymer

third_party/polymer/v1_0/components-chromium/polymer-externs/polymer.externs.js

 /**
  * @fileoverview Closure compiler externs for the Polymer library.
  *
  * @externs
  * @license
  * Copyright (c) 2015 The Polymer Project Authors. All rights reserved.
  * This code may only be used under the BSD style license found at
  * http://polymer.github.io/LICENSE.txt. The complete set of authors may be
  * found at http://polymer.github.io/AUTHORS.txt. The complete set of
  * contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt. Code
@@ skipping 617 matching lines @@
 Polymer.Templatizer = {
   /**
    * @param {?Object} model
    * @return {?Element}
    */
   stamp: function(model) {},
 
   /**
    * @param {?Element} template
    */
-  templatize: function(template) {},
+  templatize: function(template) {}
 };
 
 
 /**
  * An Event type fired when moving while finger/button is down.
  * state - a string indicating the tracking state:
  *     + start: fired when tracking is first detected (finger/button down and
  *              moved past a pre-set distance threshold)
  *     + track: fired while tracking
  *     + end: fired when tracking ends
@@ skipping 25 matching lines @@
  * y - clientY coordinate for event
  * sourceEvent - the original DOM event that caused the down action
  *
  * @typedef {{
  *   x: number,
  *   y: number,
  *   sourceEvent: Event
  * }}
  */
 var PolymerTouchEvent;