HashChangeEvent(String type, { bool canBubble: true, bool cancelable: true, String oldUrl, String newUrl })

Source 

factory HashChangeEvent(String type,
    {bool canBubble: true, bool cancelable: true, String oldUrl,
    String newUrl}) {

  // TODO(alanknight): This is required while we're on Dartium 39, but will need
  // to look like dart2js with later versions when initHashChange is removed.
  var event = document._createEvent("HashChangeEvent");
  event._initHashChangeEvent(type, canBubble, cancelable, oldUrl, newUrl);
  return event;
}