Adding second layer of the echo canceller 3 functionality.

webrtc/modules/audio_processing/test/echo_canceller_test_tools.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_TEST_ECHO_CANCELLER_TEST_TOOLS_H_
+#define WEBRTC_MODULES_AUDIO_PROCESSING_TEST_ECHO_CANCELLER_TEST_TOOLS_H_
+
+#include <algorithm>
+#include <vector>
+
+#include "webrtc/base/array_view.h"
+#include "webrtc/base/constructormagic.h"
+#include "webrtc/base/random.h"
+
+namespace webrtc {
+
+// Class for delaying a signal a fixed number of samples.
+template <typename T>
+class DelayBuffer {
+ public:
+  explicit DelayBuffer(size_t delay) : buffer_(delay) {}
+  ~DelayBuffer() = default;
+
+  // Produces a delayed signal copy of x.
+  void Delay(rtc::ArrayView<const T> x, rtc::ArrayView<T> x_delayed) {
+    RTC_DCHECK_EQ(x.size(), x_delayed.size());
+    if (buffer_.size() == 0) {
+      std::copy(std::begin(x), std::end(x), std::begin(x_delayed));
+    } else {
+      for (size_t k = 0; k < x.size(); ++k) {
+        x_delayed[k] = buffer_[next_insert_index_];
+        buffer_[next_insert_index_] = x[k];
+        next_insert_index_ = (next_insert_index_ + 1) % buffer_.size();
+      }
+    }
+  }
+
+ private:
+  std::vector<T> buffer_;
+  size_t next_insert_index_ = 0;
+  RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(DelayBuffer);
+};
+
+// Randomizes the elements in a vector with values -32767.f:32767.f.
+void RandomizeSampleVector(Random* random_generator, rtc::ArrayView<float> v);
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_AUDIO_PROCESSING_TEST_ECHO_CANCELLER_TEST_TOOLS_H_