Ensures that audio tasks cannot run after AudioManager is deleted.

media/audio/mac/audio_manager_mac.h

Index: media/audio/mac/audio_manager_mac.h
diff --git a/media/audio/mac/audio_manager_mac.h b/media/audio/mac/audio_manager_mac.h
index ae6238b958b39f7b3d081eb8581f9c47768b4f91..dc0d1a43e8c5e57c1ed900c2671396ec25ad906b 100644
--- a/media/audio/mac/audio_manager_mac.h
+++ b/media/audio/mac/audio_manager_mac.h
@@ -33,8 +33,10 @@ class MEDIA_EXPORT AudioManagerMac : public AudioManagerBase {
       scoped_refptr<base::SingleThreadTaskRunner> task_runner,
       scoped_refptr<base::SingleThreadTaskRunner> worker_task_runner,
       AudioLogFactory* audio_log_factory);
+  ~AudioManagerMac() override;
 
   // Implementation of AudioManager.
+  void Shutdown() override;
   bool HasAudioOutputDevices() override;
   bool HasAudioInputDevices() override;
   void GetAudioInputDeviceNames(AudioDeviceNames* device_names) override;
@@ -125,7 +127,6 @@ class MEDIA_EXPORT AudioManagerMac : public AudioManagerBase {
   size_t basic_input_streams() const { return basic_input_streams_.size(); }
 
  protected:
-  ~AudioManagerMac() override;
   AudioParameters GetPreferredOutputStreamParameters(
       const std::string& output_device_id,
       const AudioParameters& input_params) override;