Bug 1145403 - Don't open MediaManager on shutdown. r=jesup

dom/base/Navigator.cpp

@@ -1982,8 +1982,8 @@ Navigator::OnNavigation()
   }
 
 #ifdef MOZ_MEDIA_NAVIGATOR
-  // Inform MediaManager in case there are live streams or pending callbacks.
-  MediaManager *manager = MediaManager::Get();
+  // If MediaManager is open let it inform any live streams or pending callbacks
+  MediaManager *manager = MediaManager::GetIfExists();
   if (manager) {
     manager->OnNavigation(mWindow->WindowID());
   }

dom/media/MediaManager.cpp

@@ -1418,7 +1418,11 @@ NS_IMPL_ISUPPORTS(MediaManager, nsIMediaManagerService, nsIObserver)
 MediaManager::Get() {
   if (!sSingleton) {
     NS_ASSERTION(NS_IsMainThread(), "Only create MediaManager on main thread");
-
+#ifdef DEBUG
+    static int timesCreated = 0;
+    timesCreated++;
+    MOZ_ASSERT(timesCreated == 1);
+#endif
     sSingleton = new MediaManager();
 
     sSingleton->mMediaThread = new base::Thread("MediaManager");
@@ -1454,6 +1458,11 @@ MediaManager::Get() {
   return sSingleton;
 }
 
+/* static */  MediaManager*
+MediaManager::GetIfExists() {
+  return sSingleton;
+}
+
 /* static */ already_AddRefed<MediaManager>
 MediaManager::GetInstance()
 {

dom/media/MediaManager.h

@@ -554,6 +554,7 @@ public:
   // thread from the MainThread, as we NS_DISPATCH_SYNC to MainThread
   // from MediaManager thread.
   static MediaManager* Get();
+  static MediaManager* GetIfExists();
   static MessageLoop* GetMessageLoop();
 
   static bool Exists()