Resubmit 'Refactor the TrayAudio code so that it can be used by other platforms.'

chromeos/audio/cras_audio_handler.h

Index: chromeos/audio/cras_audio_handler.h
diff --git a/chromeos/audio/cras_audio_handler.h b/chromeos/audio/cras_audio_handler.h
index f2a35a50997af670634f77a9b71848a8a2ab7920..cc28c50f1ad408d17e54c60c47c954021d0b35a2 100644
--- a/chromeos/audio/cras_audio_handler.h
+++ b/chromeos/audio/cras_audio_handler.h
@@ -99,6 +99,9 @@ class CHROMEOS_EXPORT CrasAudioHandler : public CrasAudioClient::Observer,
   // Returns true if the output volume is below the default mute volume level.
   virtual bool IsOutputVolumeBelowDefaultMuteLvel();
 
+  // Returns volume level in 0-100% range at which the volume should be muted.
+  virtual int GetOutputDefaultVolumeMuteThreshold();
+
   // Gets volume level in 0-100% range (0 being pure silence) for the current
   // active node.
   virtual int GetOutputVolumePercent();