Add empty residual echo detector.

webrtc/modules/audio_processing/echo_detector/echo_detector.cc

 /*
  *  Copyright (c) 2016 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.
- *
  */
 
-#if !defined(RTC_DISABLE_VP9)
-#error
-#endif  // !defined(RTC_DISABLE_VP9)
-
-#include "webrtc/base/checks.h"
-#include "webrtc/modules/video_coding/codecs/vp9/include/vp9.h"
+#include "webrtc/modules/audio_processing/echo_detector/echo_detector.h"
 
 namespace webrtc {
 
-bool VP9Encoder::IsSupported() {
-  return false;
+void EchoDetector::BufferFarend(const rtc::ArrayView<const float>& /*farend*/) {
+  // TODO(ivoc): Add implementation.
+  RTC_NOTREACHED();
 }
 
-VP9Encoder* VP9Encoder::Create() {
+void EchoDetector::Process(const rtc::ArrayView<const float>& /*nearend*/) {
+  // TODO(ivoc): Add implementation.
   RTC_NOTREACHED();
-  return nullptr;
 }
 
-bool VP9Decoder::IsSupported() {
-  return false;
-}
-
-VP9Decoder* VP9Decoder::Create() {
+void EchoDetector::Initialize(int /*sample_rate_hz*/) {
+  // TODO(ivoc): Add implementation.
   RTC_NOTREACHED();
-  return nullptr;
 }
 
 }  // namespace webrtc