Roll Polymer to 1.3.1

third_party/polymer/v1_0/components-chromium/iron-menu-behavior/iron-menubar-behavior-extracted.js

 /**
    * `Polymer.IronMenubarBehavior` implements accessible menubar behavior.
    *
    * @polymerBehavior Polymer.IronMenubarBehavior
    */
   Polymer.IronMenubarBehaviorImpl = {
 
     hostAttributes: {
       'role': 'menubar'
     },
@@ skipping 10 matching lines @@
 
     _onDownKey: function(event) {
       this.focusedItem.click();
       event.detail.keyboardEvent.preventDefault();
     },
 
     get _isRTL() {
       return window.getComputedStyle(this)['direction'] === 'rtl';
     },
 
-    _onLeftKey: function() {
+    _onLeftKey: function(event) {
       if (this._isRTL) {
         this._focusNext();
       } else {
         this._focusPrevious();
       }
+      event.detail.keyboardEvent.preventDefault();
     },
 
-    _onRightKey: function() {
+    _onRightKey: function(event) {
       if (this._isRTL) {
         this._focusPrevious();
       } else {
         this._focusNext();
       }
+      event.detail.keyboardEvent.preventDefault();
     },
 
     _onKeydown: function(event) {
       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
   ];