Mixing audio with different latency requirements

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 bdffef24b6e63a9ec239b8012cdf6dc95b4ca594..1d432d40623b34caecb9952087ea35ceffb5cee5 100644
--- a/media/base/audio_renderer_mixer.h
+++ b/media/base/audio_renderer_mixer.h
@@ -26,8 +26,11 @@ namespace media {
 class MEDIA_EXPORT AudioRendererMixer
     : NON_EXPORTED_BASE(public AudioRendererSink::RenderCallback) {
  public:
+  typedef base::Callback<void(int)> UmaLogCallback;
+
   AudioRendererMixer(const AudioParameters& output_params,
-                     scoped_refptr<AudioRendererSink> sink);
+                     scoped_refptr<AudioRendererSink> sink,
+                     const UmaLogCallback& log_callback);
   ~AudioRendererMixer() override;
 
   // Add or remove a mixer input from mixing; called by AudioRendererMixerInput.
@@ -51,7 +54,11 @@ class MEDIA_EXPORT AudioRendererMixer
   // Returns true if called on rendering thread, otherwise false.
   bool CurrentThreadIsRenderingThread();
 
+  const AudioParameters& GetOutputParamsForTesting() { return output_params_; };
+
  private:
+  class UMAMaxValueTracker;
+
   // Maps input sample rate to the dedicated converter.
   using AudioConvertersMap =
       std::map<int, std::unique_ptr<LoopbackAudioConverter>>;
@@ -94,6 +101,10 @@ class MEDIA_EXPORT AudioRendererMixer
   base::TimeTicks last_play_time_;
   bool playing_;
 
+  // Tracks the maximum number of simultaneous mixer inputs and logs it into
+  // UMA histogram upon the destruction.
+  std::unique_ptr<UMAMaxValueTracker> input_count_tracker_;
+
   DISALLOW_COPY_AND_ASSIGN(AudioRendererMixer);
 };