factory constructor MessageEvent

Source

factory MessageEvent(String type,
    {bool canBubble: false,
    bool cancelable: false,
    Object data,
    String origin,
    String lastEventId,
    Window source,
    List<MessagePort> messagePorts}) {
  if (source == null) {
    source = window;
  }
  MessageEvent event = document._createEvent("MessageEvent");
  event._initMessageEvent(type, canBubble, cancelable, data, origin,
      lastEventId, source, messagePorts);
  return event;
}