Bug 780761 - Fix race condition in initialization of message manager for popups from <iframe mozbrowser>. r=smaug

Calling show() causes EnsureMessageManager() to SetCallbackData() on the message manager.  If we don't do this, then the message manager will throw when we try to send a message.

content/base/src/nsFrameLoader.cpp

@@ -2374,12 +2374,6 @@ nsFrameLoader::SetRemoteBrowser(nsITabParent* aTabParent)
   MOZ_ASSERT(!mCurrentRemoteFrame);
   mRemoteBrowser = static_cast<TabParent*>(aTabParent);
 
-  EnsureMessageManager();
-  nsCOMPtr<nsIObserverService> os = services::GetObserverService();
-  if (OwnerIsBrowserFrame() && os) {
-    mRemoteBrowserInitialized = true;
-    os->NotifyObservers(NS_ISUPPORTS_CAST(nsIFrameLoader*, this),
-                        "remote-browser-frame-shown", NULL);
-  }
+  ShowRemoteFrame(nsIntSize(0, 0));
 }