Revert of - Clean up unused voice engine DTMF code.

webrtc/voice_engine/transmit_mixer.h

Index: webrtc/voice_engine/transmit_mixer.h
diff --git a/webrtc/voice_engine/transmit_mixer.h b/webrtc/voice_engine/transmit_mixer.h
index 483af0518ab5d5e7c2092e41557bae1f27d95f22..b5c483aa4b790434b02d6516943a77a964491e1f 100644
--- a/webrtc/voice_engine/transmit_mixer.h
+++ b/webrtc/voice_engine/transmit_mixer.h
@@ -74,6 +74,9 @@
     uint32_t CaptureLevel() const;
 
     int32_t StopSend();
+
+    // VoEDtmf
+    void UpdateMuteMicrophoneTime(uint32_t lengthMs);
 
     // VoEExternalMedia
     int RegisterExternalMediaProcessing(VoEMediaProcess* object,
@@ -223,6 +226,7 @@
     VoEMediaProcess* external_postproc_ptr_;
     VoEMediaProcess* external_preproc_ptr_;
     bool _mute;
+    int32_t _remainingMuteMicTimeMs;
     bool stereo_codec_;
     bool swap_stereo_channels_;
 };