Bug 1183925 - Part 2: Clean up the AudioChannelService shutdown; r=baku

Right now this function is called after the XPCOM component manager is
shut down, so it can never remove any observers.  It's better to do this
work in response to xpcom-shutdown while we still have a component
manager to be able to clean up after ourselves properly.

dom/audiochannel/AudioChannelService.cpp

@@ -207,8 +207,7 @@ NS_IMPL_ADDREF(AudioChannelService)
 NS_IMPL_RELEASE(AudioChannelService)
 
 AudioChannelService::AudioChannelService()
-  : mDisabled(false)
-  , mDefChannelChildID(CONTENT_PROCESS_ID_UNKNOWN)
+  : mDefChannelChildID(CONTENT_PROCESS_ID_UNKNOWN)
   , mTelephonyChannel(false)
   , mContentOrNormalChannel(false)
   , mAnyChannel(false)
@@ -238,10 +237,6 @@ void
 AudioChannelService::RegisterAudioChannelAgent(AudioChannelAgent* aAgent,
                                                AudioChannel aChannel)
 {
-  if (mDisabled) {
-    return;
-  }
-
   uint64_t windowID = aAgent->WindowID();
   AudioChannelWindow* winData = GetWindowData(windowID);
   if (!winData) {
@@ -272,10 +267,6 @@ AudioChannelService::RegisterAudioChannelAgent(AudioChannelAgent* aAgent,
 void
 AudioChannelService::UnregisterAudioChannelAgent(AudioChannelAgent* aAgent)
 {
-  if (mDisabled) {
-    return;
-  }
-
   AudioChannelWindow* winData = GetWindowData(aAgent->WindowID());
   if (!winData) {
     return;
@@ -466,8 +457,8 @@ AudioChannelService::Observe(nsISupports* aSubject, const char* aTopic,
                              const char16_t* aData)
 {
   if (!strcmp(aTopic, "xpcom-shutdown")) {
-    mDisabled = true;
     mWindows.Clear();
+    Shutdown();
   }
 
 #ifdef MOZ_WIDGET_GONK

dom/audiochannel/AudioChannelService.h

@@ -43,11 +43,6 @@ public:
    */
   static already_AddRefed<AudioChannelService> GetOrCreate();
 
-  /**
-   * Shutdown the singleton.
-   */
-  static void Shutdown();
-
   static bool IsAudioChannelMutedByDefault();
 
   /**
@@ -136,6 +131,11 @@ private:
   AudioChannelService();
   ~AudioChannelService();
 
+  /**
+   * Shutdown the singleton.
+   */
+  static void Shutdown();
+
   void MaybeSendStatusUpdate();
 
   bool ContentOrNormalChannelIsActive();
@@ -204,8 +204,6 @@ private:
   nsTArray<SpeakerManagerService*>  mSpeakerManager;
 #endif
 
-  bool mDisabled;
-
   nsCOMPtr<nsIRunnable> mRunnable;
 
   uint64_t mDefChannelChildID;

layout/build/nsLayoutStatics.cpp

@@ -433,8 +433,6 @@ nsLayoutStatics::Shutdown()
   nsHyphenationManager::Shutdown();
   nsDOMMutationObserver::Shutdown();
 
-  AudioChannelService::Shutdown();
-
   DataStoreService::Shutdown();
 
   ContentParent::ShutDown();