Caching AudioOutputDevice instances in mixer manager

media/base/audio_renderer_mixer_input.h

Index: media/base/audio_renderer_mixer_input.h
diff --git a/media/base/audio_renderer_mixer_input.h b/media/base/audio_renderer_mixer_input.h
index a75320e78c681c73303c8d65bca0f9fb8a7cfd30..b23c27fc94b7feb1b5cec609511847ad2ea4383b 100644
--- a/media/base/audio_renderer_mixer_input.h
+++ b/media/base/audio_renderer_mixer_input.h
@@ -27,24 +27,15 @@
 
 namespace media {
 
+class AudioRendererMixerPool;
 class AudioRendererMixer;
 
 class MEDIA_EXPORT AudioRendererMixerInput
     : NON_EXPORTED_BASE(public SwitchableAudioRendererSink),
       public AudioConverter::InputCallback {
  public:
-  typedef base::Callback<AudioRendererMixer*(const AudioParameters& params,
-                                             const std::string& device_id,
-                                             const url::Origin& security_origin,
-                                             OutputDeviceStatus* device_status)>
-      GetMixerCB;
-  typedef base::Callback<void(const AudioParameters& params,
-                              const std::string& device_id,
-                              const url::Origin& security_origin)>
-      RemoveMixerCB;
-
-  AudioRendererMixerInput(const GetMixerCB& get_mixer_cb,
-                          const RemoveMixerCB& remove_mixer_cb,
+  AudioRendererMixerInput(AudioRendererMixerPool* mixer_pool,
+                          int owner_id,
                           const std::string& device_id,
                           const url::Origin& security_origin);
 
@@ -70,6 +61,9 @@ class MEDIA_EXPORT AudioRendererMixerInput
  private:
   friend class AudioRendererMixerInputTest;
 
+  // Pool to obtain mixers from / return them to.
+  AudioRendererMixerPool* const mixer_pool_;
+
   // Protect |volume_|, accessed by separate threads in ProvideInput() and
   // SetVolume().
   base::Lock volume_lock_;
@@ -82,20 +76,15 @@ class MEDIA_EXPORT AudioRendererMixerInput
   double ProvideInput(AudioBus* audio_bus,
                       base::TimeDelta buffer_delay) override;
 
-  // Callbacks provided during construction which allow AudioRendererMixerInput
-  // to retrieve a mixer during Initialize() and notify when it's done with it.
-  const GetMixerCB get_mixer_cb_;
-  const RemoveMixerCB remove_mixer_cb_;
-
   // AudioParameters received during Initialize().
   AudioParameters params_;
 
-  // ID of hardware device to use
-  std::string device_id_;
+  const int owner_id_;
+  std::string device_id_;  // ID of hardware device to use
   url::Origin security_origin_;
 
-  // AudioRendererMixer provided through |get_mixer_cb_| during Initialize(),
-  // guaranteed to live (at least) until |remove_mixer_cb_| is called.
+  // AudioRendererMixer obtained from mixer pool during Initialize(),
+  // guaranteed to live (at least) until it is returned to the pool.
   AudioRendererMixer* mixer_;
 
   // Source of audio data which is provided to the mixer.