Roll Polymer from 1.5.0 -> 1.6.0 to pick up native CSS custom props

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

 /**
    * `Polymer.IronMenuBehavior` implements accessible menu behavior.
    *
    * @demo demo/index.html
    * @polymerBehavior Polymer.IronMenuBehavior
    */
   Polymer.IronMenuBehaviorImpl = {
 
     properties: {
 
@@ skipping 105 matching lines @@
             title.trim().charAt(0).toLowerCase() === String.fromCharCode(event.keyCode).toLowerCase()) {
           this._setFocusedItem(item);
           break;
         }
       }
     },
 
     /**
      * Focuses the previous item (relative to the currently focused item) in the
      * menu, disabled items will be skipped.
+     * Loop until length + 1 to handle case of single item in menu.
      */
     _focusPrevious: function() {
       var length = this.items.length;
       var curFocusIndex = Number(this.indexOf(this.focusedItem));
-      for (var i = 1; i < length; i++) {
+      for (var i = 1; i < length + 1; i++) {
         var item = this.items[(curFocusIndex - i + length) % length];
         if (!item.hasAttribute('disabled')) {
           this._setFocusedItem(item);
           return;
         }
       }
     },
 
     /**
      * Focuses the next item (relative to the currently focused item) in the
      * menu, disabled items will be skipped.
+     * Loop until length + 1 to handle case of single item in menu.
      */
     _focusNext: function() {
       var length = this.items.length;
       var curFocusIndex = Number(this.indexOf(this.focusedItem));
-      for (var i = 1; i < length; i++) {
+      for (var i = 1; i < length + 1; i++) {
         var item = this.items[(curFocusIndex + i) % length];
         if (!item.hasAttribute('disabled')) {
           this._setFocusedItem(item);
           return;
         }
       }
     },
 
     /**
      * Mutates items in the menu based on provided selection details, so that
@@ skipping 150 matching lines @@
   };
 
   Polymer.IronMenuBehaviorImpl._shiftTabPressed = false;
 
   /** @polymerBehavior Polymer.IronMenuBehavior */
   Polymer.IronMenuBehavior = [
     Polymer.IronMultiSelectableBehavior,
     Polymer.IronA11yKeysBehavior,
     Polymer.IronMenuBehaviorImpl
   ];