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

modules/audio_device/linux/audio_device_alsa_linux.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 107 matching lines @@
     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;
 
     // Delay information and control
     int32_t PlayoutDelay(uint16_t& delayMS) const override;
     int32_t RecordingDelay(uint16_t& delayMS) 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;
-
     void AttachAudioBuffer(AudioDeviceBuffer* audioBuffer) override;
 
 private:
     int32_t GetDevicesInfo(const int32_t function,
                            const bool playback,
                            const int32_t enumDeviceNo = 0,
                            char* enumDeviceName = NULL,
                            const int32_t ednLen = 0) const;
     int32_t ErrorRecovery(int32_t error, snd_pcm_t* deviceHandle);
 
@@ skipping 52 matching lines @@
     bool _initialized;
     bool _recording;
     bool _playing;
     bool _recIsInitialized;
     bool _playIsInitialized;
     bool _AGC;
 
     snd_pcm_sframes_t _recordingDelay;
     snd_pcm_sframes_t _playoutDelay;
 
-    uint16_t _playWarning;
-    uint16_t _playError;
-    uint16_t _recWarning;
-    uint16_t _recError;
-
     char _oldKeyState[32];
 #if defined(USE_X11)
     Display* _XDisplay;
 #endif
 };
 
 }
 
 #endif  // MODULES_AUDIO_DEVICE_MAIN_SOURCE_LINUX_AUDIO_DEVICE_ALSA_LINUX_H_