Ensures that audio tasks cannot run after AudioManager is deleted.

media/audio/pulse/audio_manager_pulse.h

Index: media/audio/pulse/audio_manager_pulse.h
diff --git a/media/audio/pulse/audio_manager_pulse.h b/media/audio/pulse/audio_manager_pulse.h
index 662c4614a8ce97effbb19885ae7b82e8db50e2dc..bdf9e7e5bced30ccd237096bd4e025f1ed6562e1 100644
--- a/media/audio/pulse/audio_manager_pulse.h
+++ b/media/audio/pulse/audio_manager_pulse.h
@@ -21,10 +21,12 @@ class MEDIA_EXPORT AudioManagerPulse : public AudioManagerBase {
       scoped_refptr<base::SingleThreadTaskRunner> task_runner,
       scoped_refptr<base::SingleThreadTaskRunner> worker_task_runner,
       AudioLogFactory* audio_log_factory);
+  ~AudioManagerPulse() override;
 
   bool Init();
 
   // Implementation of AudioManager.
+  void Shutdown() override;
   bool HasAudioOutputDevices() override;
   bool HasAudioInputDevices() override;
   void ShowAudioInputSettings() override;
@@ -52,8 +54,6 @@ class MEDIA_EXPORT AudioManagerPulse : public AudioManagerBase {
       const LogCallback& log_callback) override;
 
  protected:
-  ~AudioManagerPulse() override;
-
   AudioParameters GetPreferredOutputStreamParameters(
       const std::string& output_device_id,
       const AudioParameters& input_params) override;