Add empty residual echo detector.

webrtc/modules/audio_processing/audio_processing_impl.h

Index: webrtc/modules/audio_processing/audio_processing_impl.h
diff --git a/webrtc/modules/audio_processing/audio_processing_impl.h b/webrtc/modules/audio_processing/audio_processing_impl.h
index be0e9518c38a06fecad89c0b9073f1451f3310a6..530c822c3bbd986c5265f48e2634e90a9997ac8e 100644
--- a/webrtc/modules/audio_processing/audio_processing_impl.h
+++ b/webrtc/modules/audio_processing/audio_processing_impl.h
@@ -148,6 +148,7 @@ class AudioProcessingImpl : public AudioProcessing {
     bool Update(bool high_pass_filter_enabled,
                 bool echo_canceller_enabled,
                 bool mobile_echo_controller_enabled,
+                bool residual_echo_detector_enabled,
                 bool noise_suppressor_enabled,
                 bool intelligibility_enhancer_enabled,
                 bool beamformer_enabled,
@@ -165,6 +166,7 @@ class AudioProcessingImpl : public AudioProcessing {
     bool high_pass_filter_enabled_ = false;
     bool echo_canceller_enabled_ = false;
     bool mobile_echo_controller_enabled_ = false;
+    bool residual_echo_detector_enabled_ = false;
     bool noise_suppressor_enabled_ = false;
     bool intelligibility_enhancer_enabled_ = false;
     bool beamformer_enabled_ = false;
@@ -232,6 +234,8 @@ class AudioProcessingImpl : public AudioProcessing {
   int InitializeLocked(const ProcessingConfig& config)
       EXCLUSIVE_LOCKS_REQUIRED(crit_render_, crit_capture_);
   void InitializeLevelController() EXCLUSIVE_LOCKS_REQUIRED(crit_capture_);
+  void InitializeResidualEchoDetector()
+      EXCLUSIVE_LOCKS_REQUIRED(crit_render_, crit_capture_);
 
   // Capture-side exclusive methods possibly running APM in a multi-threaded
   // manner that are called with the render lock already acquired.