Prepare to remove ADM APIs that are to be deprecated.

modules/audio_device/include/audio_device.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 34 matching lines @@
     kChannelRight = 1,
     kChannelBoth = 2
   };
 
  public:
   // Create an ADM.
   static rtc::scoped_refptr<AudioDeviceModule> Create(
       const int32_t id,
       const AudioLayer audio_layer);
 
+  // TODO(solenberg): Remove temporary implementation of Module interface.
+  int64_t TimeUntilNextProcess() override {
+    // Make sure Process() isn't called very often.
+    return 1000000;
+  }
+  void Process() override {}
+
   // Retrieve the currently utilized audio layer
   virtual int32_t ActiveAudioLayer(AudioLayer* audioLayer) const = 0;
 
   // Error handling
   virtual ErrorCode LastError() const = 0;
-  virtual int32_t RegisterEventObserver(AudioDeviceObserver* eventCallback) = 0;
+  virtual int32_t RegisterEventObserver(AudioDeviceObserver* eventCallback) {
+    return 0;
+  }
 
   // Full-duplex transportation of PCM audio
   virtual int32_t RegisterAudioCallback(AudioTransport* audioCallback) = 0;
 
   // Main initialization and termination
   virtual int32_t Init() = 0;
   virtual int32_t Terminate() = 0;
   virtual bool Initialized() const = 0;
 
   // Device enumeration
@@ skipping 102 matching lines @@
   virtual int GetRecordAudioParameters(AudioParameters* params) const = 0;
 #endif  // WEBRTC_IOS
 
  protected:
   ~AudioDeviceModule() override {}
 };
 
 }  // namespace webrtc
 
 #endif  // MODULES_AUDIO_DEVICE_INCLUDE_AUDIO_DEVICE_H_