Add algorithm for Residual Echo Detector.

webrtc/modules/audio_processing/echo_detector/circular_buffer.h

Index: webrtc/modules/audio_processing/echo_detector/circular_buffer.h
diff --git a/webrtc/modules/audio_processing/echo_detector/circular_buffer.h b/webrtc/modules/audio_processing/echo_detector/circular_buffer.h
new file mode 100644
index 0000000000000000000000000000000000000000..667b1f882429b8c0fd6ec5e8bc994d5e60968626
--- /dev/null
+++ b/webrtc/modules/audio_processing/echo_detector/circular_buffer.h
@@ -0,0 +1,42 @@
+/*
+ *  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.
+ */
+
+#ifndef WEBRTC_MODULES_AUDIO_PROCESSING_ECHO_DETECTOR_CIRCULAR_BUFFER_H_
+#define WEBRTC_MODULES_AUDIO_PROCESSING_ECHO_DETECTOR_CIRCULAR_BUFFER_H_
+
+#include <vector>
+
+#include "webrtc/base/optional.h"
+
+namespace webrtc {
+
+// Ring buffer containing floating point values.
+struct CircularBuffer {
+ public:
+  explicit CircularBuffer(size_t size);
+  ~CircularBuffer();
+
+  void Push(float value);
+  rtc::Optional<float> Pop();
+  size_t Size() const { return nr_elements_in_buffer_; }
+  // This function fills the buffer with zeros, but does not change its size.
+  void Clear();
+
+ private:
+  std::vector<float> buffer_;
+  size_t next_insertion_index_ = 0;
+  // This is the number of elements that have been pushed into the circular
+  // buffer, not the allocated buffer size.
+  size_t nr_elements_in_buffer_ = 0;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_AUDIO_PROCESSING_ECHO_DETECTOR_CIRCULAR_BUFFER_H_