Prepare to remove ADM APIs that are to be deprecated.

modules/audio_device/include/audio_device.h

Index: modules/audio_device/include/audio_device.h
diff --git a/modules/audio_device/include/audio_device.h b/modules/audio_device/include/audio_device.h
index 8751b8e58931d7d3e8a066065300c68487d79ae1..b378f9ffce17bf7f9cb5df1f00ef59980d52e5f7 100644
--- a/modules/audio_device/include/audio_device.h
+++ b/modules/audio_device/include/audio_device.h
@@ -52,12 +52,21 @@ class AudioDeviceModule : public RefCountedModule {
       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;