Remove the VoiceEngineObserver callback interface.

audio/audio_state.h

 /*
  *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #ifndef AUDIO_AUDIO_STATE_H_
 #define AUDIO_AUDIO_STATE_H_
 
 #include "audio/audio_transport_proxy.h"
 #include "audio/scoped_voe_interface.h"
 #include "call/audio_state.h"
 #include "rtc_base/constructormagic.h"
 #include "rtc_base/criticalsection.h"
 #include "rtc_base/thread_checker.h"
 #include "voice_engine/include/voe_base.h"
 
 namespace webrtc {
 namespace internal {
 
-class AudioState final : public webrtc::AudioState,
-                         public webrtc::VoiceEngineObserver {
+class AudioState final : public webrtc::AudioState {
  public:
   explicit AudioState(const AudioState::Config& config);
   ~AudioState() override;
 
   AudioProcessing* audio_processing() override {
     RTC_DCHECK(config_.audio_processing);
     return config_.audio_processing.get();
   }
 
   VoiceEngine* voice_engine();
   rtc::scoped_refptr<AudioMixer> mixer();
   bool typing_noise_detected() const;
 
  private:
   // rtc::RefCountInterface implementation.
   int AddRef() const override;
   int Release() const override;
 
-  // webrtc::VoiceEngineObserver implementation.
-  void CallbackOnError(int channel_id, int err_code) override;
-
   rtc::ThreadChecker thread_checker_;
   rtc::ThreadChecker process_thread_checker_;
   const webrtc::AudioState::Config config_;
 
   // We hold one interface pointer to the VoE to make sure it is kept alive.
   ScopedVoEInterface<VoEBase> voe_base_;
 
-  // The critical section isn't strictly needed in this case, but xSAN bots may
-  // trigger on unprotected cross-thread access.
-  rtc::CriticalSection crit_sect_;
-  bool typing_noise_detected_ RTC_GUARDED_BY(crit_sect_) = false;
-
   // Reference count; implementation copied from rtc::RefCountedObject.
   mutable volatile int ref_count_ = 0;
 
   // Transports mixed audio from the mixer to the audio device and
   // recorded audio to the VoE AudioTransport.
   AudioTransportProxy audio_transport_proxy_;
 
   RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(AudioState);
 };
 }  // namespace internal
 }  // namespace webrtc
 
 #endif  // AUDIO_AUDIO_STATE_H_