fire_ (eventName, detail=null, bubbles=true, cancelable=true) {
    let evt = new CustomEvent(eventName, { detail, bubbles, cancelable });
    this.element_.dispatchEvent(evt);
  }
Fires an event on the element.

@private
@param {String} eventName - The name of the event.
@param {} [detail=null] - The data to include in the event.
@param {Boolean} [bubbles=true] - Whether the event should bubble.
@param {Boolean} [cancelable=true] - Whether the event is cancelable.