code: function HeadlessEvent(type, opt_bubbles, opt_preventable) {
        this.type = type;
        this.bubbles = (opt_bubbles !== undefined ?
            !!opt_bubbles : false);
        this.cancelable = (opt_preventable !== undefined ?
            !!opt_preventable : false);
  
        this.defaultPrevented = false;
        this.cancelBubble = false;
      }
docs: Creates a new event to be used with tr.b.EventTarget or DOM EventTarget
  objects.
  @param {string} type The name of the event.
  @param {boolean=} opt_bubbles Whether the event bubbles.
  Default is false.
  @param {boolean=} opt_preventable Whether the default action of the event
  can be prevented.
  @constructor
  @extends {Event}