AudioManagerBase: Create and run the audio thread lazily.

media/audio/audio_manager_base.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MEDIA_AUDIO_AUDIO_MANAGER_BASE_H_
 #define MEDIA_AUDIO_AUDIO_MANAGER_BASE_H_
 
 #include <string>
 #include <utility>
 
@@ skipping 34 matching lines @@
   // default playback device. At the moment this feature is supported only on
   // some platforms. AudioInputStream::Intialize() will return an error on
   // platforms that don't support it. GetInputStreamParameters() must be used
   // to get the parameters of the loopback device before creating a loopback
   // stream, otherwise stream initialization may fail.
   static const char kLoopbackInputDeviceId[];
 
   ~AudioManagerBase() override;
 
   // AudioManager:
-  scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner() const override;
+  scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner() override;
   scoped_refptr<base::SingleThreadTaskRunner> GetWorkerTaskRunner() override;
   base::string16 GetAudioInputDeviceModel() override;
   void ShowAudioInputSettings() override;
   void GetAudioInputDeviceNames(AudioDeviceNames* device_names) override;
   void GetAudioOutputDeviceNames(AudioDeviceNames* device_names) override;
   AudioOutputStream* MakeAudioOutputStream(
       const AudioParameters& params,
       const std::string& device_id) override;
   AudioInputStream* MakeAudioInputStream(const AudioParameters& params,
                                          const std::string& device_id) override;
@@ skipping 98 matching lines @@
   // Number of currently open output streams.
   int num_output_streams_;
 
   // Number of currently open input streams.
   int num_input_streams_;
 
   // Track output state change listeners.
   base::ObserverList<AudioDeviceListener> output_listeners_;
 
   // Thread used to interact with audio streams created by this audio manager.
-  base::Thread audio_thread_;
-
-  // The task runner of the audio thread this object runs on. Used for internal
-  // tasks which run on the audio thread even after Shutdown() has been started
-  // and GetTaskRunner() starts returning NULL.
-  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+  scoped_ptr<base::Thread> audio_thread_;
 
   // Map of cached AudioOutputDispatcher instances.  Must only be touched
   // from the audio thread (no locking).
   AudioOutputDispatchers output_dispatchers_;
 
   // Proxy for creating AudioLog objects.
   AudioLogFactory* const audio_log_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioManagerBase);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_AUDIO_MANAGER_BASE_H_