Ensures that audio tasks cannot run after AudioManager is deleted.

media/audio/mock_audio_manager.h

Index: media/audio/mock_audio_manager.h
diff --git a/media/audio/mock_audio_manager.h b/media/audio/mock_audio_manager.h
index 69e0d1496ed022a37cd159da08c1bd7c09d73662..e4555e3726c0a6ef9e6c59a46e4f7e60b443e2ec 100644
--- a/media/audio/mock_audio_manager.h
+++ b/media/audio/mock_audio_manager.h
@@ -18,17 +18,14 @@ namespace media {
 // would causing failures on classes which expect that.
 class MockAudioManager : public AudioManager {
  public:
-  class Deleter {
-   public:
-    void operator()(const MockAudioManager* instance) const;
-  };
-
-  using UniquePtr = std::unique_ptr<MockAudioManager, Deleter>;
   using GetDeviceDescriptionsCallback =
       base::RepeatingCallback<void(AudioDeviceDescriptions*)>;
 
   explicit MockAudioManager(
       scoped_refptr<base::SingleThreadTaskRunner> task_runner);
+  ~MockAudioManager() override;
+
+  void Shutdown() override;
 
   bool HasAudioOutputDevices() override;
 
@@ -91,12 +88,7 @@ class MockAudioManager : public AudioManager {
   void SetOutputDeviceDescriptionsCallback(
       GetDeviceDescriptionsCallback callback);
 
- protected:
-  ~MockAudioManager() override;
-
  private:
-  friend class base::DeleteHelper<MockAudioManager>;
-
   AudioParameters input_params_;
   AudioParameters output_params_;
   AudioParameters default_output_params_;