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;
}