Deliver RenderCallbackErrors even when mixer inputs are paused.

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 942c61fe8495cd3b0a921bf0a12dc7da10269b29..9ba59b89f5034698ed435a2a2aebf0d6e50b1163 100644
--- a/media/base/audio_renderer_mixer.h
+++ b/media/base/audio_renderer_mixer.h
@@ -26,10 +26,15 @@ class MEDIA_EXPORT AudioRendererMixer
   virtual ~AudioRendererMixer();
 
   // Add or remove a mixer input from mixing; called by AudioRendererMixerInput.
-  void AddMixerInput(AudioConverter::InputCallback* input,
-                     const base::Closure& error_cb);
+  void AddMixerInput(AudioConverter::InputCallback* input);
   void RemoveMixerInput(AudioConverter::InputCallback* input);
 
+  // Since errors may occur even when no inputs are playing, an error callback
+  // must be registered separately from adding a mixer.
+  void RegisterErrorCallback(AudioConverter::InputCallback* input,
+                             const base::Closure& error_cb);
+  void UnregisterErrorCallback(AudioConverter::InputCallback* input);
+
   void set_pause_delay_for_testing(base::TimeDelta delay) {
     pause_delay_ = delay;
   }
@@ -43,12 +48,13 @@ class MEDIA_EXPORT AudioRendererMixer
   // Output sink for this mixer.
   scoped_refptr<AudioRendererSink> audio_sink_;
 
-  // Set of mixer inputs to be mixed by this mixer.  Access is thread-safe
-  // through |mixer_inputs_lock_|.
+  // ---------------[ All variables below protected by |lock_| ]---------------
+  base::Lock lock_;
+
+  // Set of error callbacks used by this mixer.
   typedef std::map<AudioConverter::InputCallback*, base::Closure>
-      AudioRendererMixerInputSet;
-  AudioRendererMixerInputSet mixer_inputs_;
-  base::Lock mixer_inputs_lock_;
+      AudioRendererMixerErrorCallbackMap;
+  AudioRendererMixerErrorCallbackMap error_callbacks_;
 
   // Handles mixing and resampling between input and output parameters.
   AudioConverter audio_converter_;