Implement the NackModule as part of the new jitter buffer.

webrtc/modules/video_coding/histogram.h

+/*
+ *  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_VIDEO_CODING_HISTOGRAM_H_
+#define WEBRTC_MODULES_VIDEO_CODING_HISTOGRAM_H_
+
+#include <vector>
+
+namespace webrtc {
+namespace video_coding {
+class Histogram {
+ public:
+  // A discrete histogram where every bucket with range [0, num_buckets).
+  // Values greater or equal to num_buckets will be placed in the last bucket.
+  Histogram(size_t num_buckets, size_t max_num_values);
+
+  // Add a value to the histogram. If there already is max_num_values in the
+  // histogram then the oldest value will be replaced with the new value.
+  void Add(size_t value);
+
+  // Calculates how many buckets have to be summed in order to accumulate at
+  // least the given probability.
+  size_t InverseCdf(float probability) const;
+
+  // How many values that make up this histogram.
+  size_t NumValues() const;
+
+ private:
+  // A circular buffer that holds the values that make up the histogram.
+  std::vector<size_t> values_;
+  std::vector<size_t> buckets_;
+  size_t index_;
+};
+
+}  // namespace video_coding
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_VIDEO_CODING_HISTOGRAM_H_