Adding second layer of the echo canceller 3 functionality.

webrtc/modules/audio_processing/aec3/echo_path_delay_estimator.h

+/*
+ *  Copyright (c) 2017 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.
+ */
+
+#ifndef WEBRTC_MODULES_AUDIO_PROCESSING_AEC3_ECHO_PATH_DELAY_ESTIMATOR_H_
+#define WEBRTC_MODULES_AUDIO_PROCESSING_AEC3_ECHO_PATH_DELAY_ESTIMATOR_H_
+
+#include <vector>
+
+#include "webrtc/base/constructormagic.h"
+#include "webrtc/base/optional.h"
+
+namespace webrtc {
+
+class ApmDataDumper;
+
+class EchoPathDelayEstimator {
+ public:
+  EchoPathDelayEstimator(ApmDataDumper* data_dumper, int sample_rate_hz);
+  ~EchoPathDelayEstimator();
+  rtc::Optional<size_t> EstimateDelay(rtc::ArrayView<const float> render,
+                                      rtc::ArrayView<const float> capture);
+
+ private:
+  RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(EchoPathDelayEstimator);
+};
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_AUDIO_PROCESSING_AEC3_ECHO_PATH_DELAY_ESTIMATOR_H_