scope handling fix (wip)

Author: rbri

src/main/java/org/htmlunit/javascript/host/BroadcastChannel.java

@@ -155,7 +155,7 @@ public void postMessage(final Object message) {
 
                         final MessageEvent event = new MessageEvent();
                         event.initMessageEvent(Event.TYPE_MESSAGE, false, false, message, origin, "", null, ports);
-                        event.setParentScope(channelWindow);
+                        event.setParentScope(channelWebWindow.getTopLevelScope());
                         event.setPrototype(channelWindow.getPrototype(event.getClass()));
 
                         final PostponedAction action =