     }
      this._w = this.$.toggleBar.offsetWidth / 2;
      e.preventTap();
    },

    trackx: function(e) {
      this._x = Math.min(this._w, 
          Math.max(0, this.checked ? this._w + e.dx : e.dx));
      this.$.toggleButton.classList.add('dragging');
      var s =  this.$.toggleButton.style;
      s.webkitTransform = s.transform = 'translate3d(' + this._x + 'px,0,0)';
    },

    trackEnd: function() {
      var s =  this.$.toggleButton.style;
      s.transform = s.webkitTransform = '';
      th