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

modules/audio_device/audio_device_buffer.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 10 matching lines @@
 #include "typedefs.h"  // NOLINT(build/include)
 
 namespace webrtc {
 
 // Delta times between two successive playout callbacks are limited to this
 // value before added to an internal array.
 const size_t kMaxDeltaTimeInMs = 500;
 // TODO(henrika): remove when no longer used by external client.
 const size_t kMaxBufferSizeBytes = 3840;  // 10ms in stereo @ 96kHz
 
-class AudioDeviceObserver;
-
 class AudioDeviceBuffer {
  public:
   enum LogState {
     LOG_START = 0,
     LOG_STOP,
     LOG_ACTIVE,
   };
 
   struct Stats {
     void ResetRecStats() {
@@ skipping 211 matching lines @@
 // Should *never* be defined in production builds. Only used for testing.
 // When defined, the output signal will be replaced by a sinus tone at 440Hz.
 #ifdef AUDIO_DEVICE_PLAYS_SINUS_TONE
   double phase_ RTC_ACCESS_ON(playout_thread_checker_);
 #endif
 };
 
 }  // namespace webrtc
 
 #endif  // MODULES_AUDIO_DEVICE_AUDIO_DEVICE_BUFFER_H_