[third_party] add polymer 1.2.3

polymer_1.2.3/bower_components/iron-menu-behavior/iron-menubar-behavior.html

 <!--
 @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 distributed by Google as part of the polymer project is also
 subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
 -->
 
@@ skipping 12 matching lines @@
     hostAttributes: {
       'role': 'menubar'
     },
 
     keyBindings: {
       'left': '_onLeftKey',
       'right': '_onRightKey'
     },
 
     _onUpKey: function(event) {
-      this._activateFocused(event.detail.keyboardEvent);
+      this.focusedItem.click();
+      event.detail.keyboardEvent.preventDefault();
     },
 
     _onDownKey: function(event) {
-      this._activateFocused(event.detail.keyboardEvent);
+      this.focusedItem.click();
+      event.detail.keyboardEvent.preventDefault();
     },
 
     _onLeftKey: function() {
       this._focusPrevious();
     },
 
     _onRightKey: function() {
       this._focusNext();
     },
 
     _onKeydown: function(event) {
-      if (this.keyboardEventMatchesKeys(event, 'up down left right esc enter')) {
+      if (this.keyboardEventMatchesKeys(event, 'up down left right esc')) {
         return;
       }
 
       // all other keys focus the menu item starting with that character
       this._focusWithKeyboardEvent(event);
     }
 
   };
 
   /** @polymerBehavior Polymer.IronMenubarBehavior */
   Polymer.IronMenubarBehavior = [
     Polymer.IronMenuBehavior,
     Polymer.IronMenubarBehaviorImpl
   ];
 
 </script>