Add empty residual echo detector.

webrtc/modules/audio_processing/echo_detector/echo_detector.cc

Index: webrtc/modules/audio_processing/echo_detector/echo_detector.cc
diff --git a/webrtc/modules/video_coding/codecs/vp9/vp9_noop.cc b/webrtc/modules/audio_processing/echo_detector/echo_detector.cc
similarity index 51%
copy from webrtc/modules/video_coding/codecs/vp9/vp9_noop.cc
copy to webrtc/modules/audio_processing/echo_detector/echo_detector.cc
index cc37e1adbbd47b91a73ea6624a86cedef7a7231f..22dcd7cb628ce50652c04893dc94c0d358a5644a 100644
--- a/webrtc/modules/video_coding/codecs/vp9/vp9_noop.cc
+++ b/webrtc/modules/audio_processing/echo_detector/echo_detector.cc
@@ -6,34 +6,23 @@
  *  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)

[ivoc, 2016/10/12 15:40:13]

Same here.

-#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;
-}
-
-VP9Encoder* VP9Encoder::Create() {
-  RTC_NOTREACHED();
-  return nullptr;
+void EchoDetector::BufferFarend(const float* /*farend*/,
+                                size_t /*nrOfSamples*/) {
+  // TODO(ivoc): Add implementation.
 }
 
-bool VP9Decoder::IsSupported() {
-  return false;
+void EchoDetector::Process(const float* /*nearend*/, size_t /*nrOfSamples*/) {
+  // TODO(ivoc): Add implementation.
 }
 
-VP9Decoder* VP9Decoder::Create() {
-  RTC_NOTREACHED();
-  return nullptr;
+void EchoDetector::Initialize(int /*sample_rate_hz*/) {
+  // TODO(ivoc): Add implementation.
 }
 
 }  // namespace webrtc