Caching AudioOutputDevice instances in mixer manager

media/base/audio_renderer_mixer.h

Index: media/base/audio_renderer_mixer.h
diff --git a/media/base/audio_renderer_mixer.h b/media/base/audio_renderer_mixer.h
index 7a6c1dd781bb96572e51dd71bbe96247d6ae6566..5b56cd1193518320c5d749b1ac91b0d9195006ba 100644
--- a/media/base/audio_renderer_mixer.h
+++ b/media/base/audio_renderer_mixer.h
@@ -27,7 +27,7 @@ class MEDIA_EXPORT AudioRendererMixer
     : NON_EXPORTED_BASE(public AudioRendererSink::RenderCallback) {
  public:
   AudioRendererMixer(const AudioParameters& output_params,
-                     const scoped_refptr<AudioRendererSink>& sink);
+                     scoped_refptr<AudioRendererSink> sink);
   ~AudioRendererMixer() override;
 
   // Add or remove a mixer input from mixing; called by AudioRendererMixerInput.
@@ -48,6 +48,9 @@ class MEDIA_EXPORT AudioRendererMixer
 
   OutputDeviceInfo GetOutputDeviceInfo();
 
+  // Used by AudioRendererMixerManager to remove mixer sink from the sink cache.

[DaleCurtis, 2016/05/23 18:29:08]

This isn't necessary, just have the ARMM store the sink as part of the MixerKey.

[o1ka, 2016/05/23 19:21:35]

Well, I don feel like it's any better to store it in one more place. Do you
insist?

[DaleCurtis, 2016/05/23 20:20:26]

I do in this case. Can you explain why you think it's equivalent? In one
instance you're adding a new public API where as the other is a private detail
to ARMM.

[o1ka, 2016/05/24 15:00:41]

Ok, the one without an interface is nicer. (added pointer to the mixer
reference)

+  const AudioRendererSink* sink_ptr() { return audio_sink_.get(); };
+
  private:
   // Maps input sample rate to the dedicated converter.
   using AudioConvertersMap =
@@ -63,11 +66,11 @@ class MEDIA_EXPORT AudioRendererMixer
     return sample_rate == output_params_.sample_rate();
   }
 
-  // Output sink for this mixer.
-  scoped_refptr<AudioRendererSink> audio_sink_;
-
   // Output parameters for this mixer.
-  AudioParameters output_params_;
+  const AudioParameters output_params_;
+
+  // Output sink for this mixer.
+  const scoped_refptr<AudioRendererSink> audio_sink_;
 
   // ---------------[ All variables below protected by |lock_| ]---------------
   base::Lock lock_;