Avoid clicks when muting/unmuting a voe::Channel.

webrtc/voice_engine/channel.h

Index: webrtc/voice_engine/channel.h
diff --git a/webrtc/voice_engine/channel.h b/webrtc/voice_engine/channel.h
index 7d9a17fcf39c86b79fd33b8a9289cf6d9b00cc2a..07a0f789da8f22c907658f8e0ca838f8c7d975e5 100644
--- a/webrtc/voice_engine/channel.h
+++ b/webrtc/voice_engine/channel.h
@@ -269,8 +269,8 @@ class Channel
   // VoEVolumeControl
   int GetSpeechOutputLevel(uint32_t& level) const;
   int GetSpeechOutputLevelFullRange(uint32_t& level) const;
-  int SetMute(bool enable);
-  bool Mute() const;
+  int SetInputMute(bool enable);
+  bool InputMute() const;
   int SetOutputVolumePan(float left, float right);
   int GetOutputVolumePan(float& left, float& right) const;
   int SetChannelOutputVolumeScaling(float scaling);
@@ -536,10 +536,11 @@ class Channel
   bool _externalMixing;
   bool _mixFileWithMicrophone;
   // VoEVolumeControl
-  bool _mute;
-  float _panLeft;
-  float _panRight;
-  float _outputGain;
+  bool input_mute_ GUARDED_BY(volume_settings_critsect_);
+  bool previous_frame_muted_;  // Only accessed from PrepareEncodeAndSend().
+  float _panLeft GUARDED_BY(volume_settings_critsect_);
+  float _panRight GUARDED_BY(volume_settings_critsect_);
+  float _outputGain GUARDED_BY(volume_settings_critsect_);
   // VoeRTP_RTCP
   uint32_t _lastLocalTimeStamp;
   int8_t _lastPayloadType;