Bug 1964075 - use the correct EventTarget when creating a MessageEvent, r=baku

Differential Revision: https://phabricator.services.mozilla.com/D248270

dom/events/Event.cpp

@@ -462,6 +462,7 @@ void Event::PreventDefault(JSContext* aCx, CallerType aCallerType) {
 void Event::PreventDefaultInternal(bool aCalledByDefaultHandler,
                                    nsIPrincipal* aPrincipal) {
   if (mEvent->mFlags.mInPassiveListener) {
+    if (mOwner) {
       if (nsPIDOMWindowInner* win = mOwner->GetAsInnerWindow()) {
         if (Document* doc = win->GetExtantDoc()) {
           if (!doc->HasWarnedAbout(
@@ -473,6 +474,7 @@ void Event::PreventDefaultInternal(bool aCalledByDefaultHandler,
           }
         }
       }
+    }
     return;
   }
   if (!mEvent->mFlags.mCancelable) {

dom/messagechannel/MessagePort.cpp

@@ -119,8 +119,7 @@ class PostMessageRunnable final : public CancelableRunnable {
     }
 
     // Create the event
-    RefPtr<MessageEvent> event =
-        new MessageEvent(mPort->GetOwnerWindow(), nullptr, nullptr);
+    RefPtr<MessageEvent> event = new MessageEvent(mPort, nullptr, nullptr);
 
     Sequence<OwningNonNull<MessagePort>> ports;
     if (!mData->TakeTransferredPortsAsSequence(ports)) {