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..77f4e75a2bb869413bb87d39eb99c7c59b30ce16 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.
+  const AudioRendererSink* sink_ptr() { return audio_sink_.get(); };
+
  private:
   // Maps input sample rate to the dedicated converter.
   using AudioConvertersMap =
@@ -64,10 +67,10 @@ class MEDIA_EXPORT AudioRendererMixer
   }
 
   // Output sink for this mixer.
-  scoped_refptr<AudioRendererSink> audio_sink_;
+  const scoped_refptr<AudioRendererSink> audio_sink_;
 
   // Output parameters for this mixer.
-  AudioParameters output_params_;
+  const AudioParameters output_params_;
 
   // ---------------[ All variables below protected by |lock_| ]---------------
   base::Lock lock_;