Remove AudioDeviceObserver and make ADM not inherit from the Module interface.

modules/audio_device/ios/audio_device_ios.h

 /*
  *  Copyright (c) 2012 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.
  */
 
@@ skipping 121 matching lines @@
   int32_t MicrophoneMute(bool& enabled) const override;
   int32_t SpeakerMuteIsAvailable(bool& available) override;
   int32_t SetSpeakerMute(bool enable) override;
   int32_t SpeakerMute(bool& enabled) const override;
   int32_t StereoPlayoutIsAvailable(bool& available) override;
   int32_t SetStereoPlayout(bool enable) override;
   int32_t StereoPlayout(bool& enabled) const override;
   int32_t StereoRecordingIsAvailable(bool& available) override;
   int32_t SetStereoRecording(bool enable) override;
   int32_t StereoRecording(bool& enabled) const override;
-  bool PlayoutWarning() const override;
-  bool PlayoutError() const override;
-  bool RecordingWarning() const override;
-  bool RecordingError() const override;
-  void ClearPlayoutWarning() override {}
-  void ClearPlayoutError() override {}
-  void ClearRecordingWarning() override {}
-  void ClearRecordingError() override {}
 
   // AudioSessionObserver methods. May be called from any thread.
   void OnInterruptionBegin() override;
   void OnInterruptionEnd() override;
   void OnValidRouteChange() override;
   void OnCanPlayOrRecordChange(bool can_play_or_record) override;
   void OnChangedOutputVolume() override;
 
   // VoiceProcessingAudioUnitObserver methods.
   OSStatus OnDeliverRecordedData(AudioUnitRenderActionFlags* flags,
@@ skipping 138 matching lines @@
   // Contains the time for when the last output volume change was detected.
   int64_t last_output_volume_change_time_ RTC_ACCESS_ON(thread_checker_);
 
   // Exposes private members for testing purposes only.
   FRIEND_TEST_ALL_PREFIXES(AudioDeviceTest, testInterruptedAudioSession);
 };
 
 }  // namespace webrtc
 
 #endif  // MODULES_AUDIO_DEVICE_IOS_AUDIO_DEVICE_IOS_H_