Ensures that audio tasks cannot run after AudioManager is deleted.

media/audio/audio_manager_base.h

Index: media/audio/audio_manager_base.h
diff --git a/media/audio/audio_manager_base.h b/media/audio/audio_manager_base.h
index a80f63c1aef6b8b5150aadb7a7b077907f37bf4c..1ba6c77f31bb6790a77d1f4f6d64f5ccf71bf16a 100644
--- a/media/audio/audio_manager_base.h
+++ b/media/audio/audio_manager_base.h
@@ -35,6 +35,7 @@ class MEDIA_EXPORT AudioManagerBase : public AudioManager {
   ~AudioManagerBase() override;
 
   // AudioManager:
+  void Shutdown() override;
   base::string16 GetAudioInputDeviceModel() override;
   void ShowAudioInputSettings() override;
 
@@ -116,12 +117,6 @@ class MEDIA_EXPORT AudioManagerBase : public AudioManager {
       scoped_refptr<base::SingleThreadTaskRunner> worker_task_runner,
       AudioLogFactory* audio_log_factory);
 
-  // Releases all the audio output dispatchers.
-  // All audio streams should be closed before Shutdown() is called.
-  // This must be called in the destructor of every AudioManagerBase
-  // implementation.
-  void Shutdown();
-
   void SetMaxOutputStreamsAllowed(int max) { max_num_output_streams_ = max; }
 
   // Called by each platform specific AudioManager to notify output state change