Bug 1308956 - Get rid of MessagePortList - part 1 - MessagePortList removed from events, r=smaug

dom/base/PostMessageEvent.cpp

@@ -150,9 +150,7 @@ PostMessageEvent::Run()
                           EmptyString(), source, nullptr);
 
   nsTArray<RefPtr<MessagePort>> ports = TakeTransferredPorts();
-
-  event->SetPorts(new MessagePortList(static_cast<dom::Event*>(event.get()),
-                                      ports));
+  event->SetPorts(Move(ports));
 
   // We can't simply call dispatchEvent on the window because doing so ends
   // up flipping the trusted bit on the event, and we don't want that to