true, close the
         * dropdown.
         *
         * @param {boolean} disabled True if disabled, otherwise false.
         */
        _disabledChanged: function(disabled) {
          Polymer.IronControlState._disabledChanged.apply(this, arguments);
          if (disabled && this.opened) {
            this.close();
          }
        },

        __onIronOverlayCanceled: function(event) {
          var uiEvent = event.detail;
          var target = Polymer.dom(uiEvent).rootTarget;
          var trigger