Fix the audio mute button broken issue.

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 54afeb81350167f18f1f90500ab84d55ca6ab275..f9da570aa2b8c06b7730ec673519f20f8f4bc04d 100644
--- a/chromeos/audio/cras_audio_handler.h
+++ b/chromeos/audio/cras_audio_handler.h
@@ -105,6 +105,9 @@ class CHROMEOS_EXPORT CrasAudioHandler : public CrasAudioClient::Observer,
   // Returns true if audio input is muted for a device.
   virtual bool IsInputMutedForDevice(uint64 device_id);
 
+  // Returns true if the output volume is below the default mute volume level.
+  virtual bool IsOutputVolumeBelowDefaultMuteLvel();
+
   // Gets volume level in 0-100% range (0 being pure silence) for the current
   // active node.
   virtual int GetOutputVolumePercent();
@@ -145,6 +148,9 @@ class CHROMEOS_EXPORT CrasAudioHandler : public CrasAudioClient::Observer,
   // Adjusts volume up (positive percentage) or down (negative percentage).
   virtual void AdjustOutputVolumeByPercent(int adjust_by_percent);
 
+  // Adjusts output volume to a minimum audible level if it is too low.
+  virtual void AdjustOutputVolumeToAudibleLevel();
+
   // Mutes or unmutes audio output device.
   virtual void SetOutputMute(bool mute_on);
 
@@ -198,12 +204,17 @@ class CHROMEOS_EXPORT CrasAudioHandler : public CrasAudioClient::Observer,
   // Sets output volume to specified value of |volume|.
   void SetOutputVolumeInternal(int volume);
 
-  // Sets output mute state to |mute_on|.
+  // Sets output mute state to |mute_on| internally, returns true if output mute
+  // is set.
   bool SetOutputMuteInternal(bool mute_on);
 
   // Sets output volume to specified value and notifies observers.
   void SetInputGainInternal(int gain);
 
+  // Sets input mute state to |mute_on| internally, returns true if input mute
+  // is set.
+  bool SetInputMuteInternal(bool mute_on);
+
   // Calling dbus to get nodes data.
   void GetNodes();