code: function dispatchSimpleEvent(target, type, opt_bubbles, opt_cancelable) {
      var e = new tr.b.Event(type, opt_bubbles, opt_cancelable);
      return target.dispatchEvent(e);
    }
docs: Dispatches a simple event on an event target.
  @param {!EventTarget} target The event target to dispatch the event on.
  @param {string} type The type of the event.
  @param {boolean=} opt_bubbles Whether the event bubbles or not.
  @param {boolean=} opt_cancelable Whether the default action of the event
  can be prevented.
  @return {boolean} If any of the listeners called {@code preventDefault}
  during the dispatch this will return false.