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diff --git a/third_party/libwebrtc/modules/audio_coding/neteq/histogram.h b/third_party/libwebrtc/modules/audio_coding/neteq/histogram.h
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+++ b/third_party/libwebrtc/modules/audio_coding/neteq/histogram.h
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+/*
+ *  Copyright (c) 2019 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 MODULES_AUDIO_CODING_NETEQ_HISTOGRAM_H_
+#define MODULES_AUDIO_CODING_NETEQ_HISTOGRAM_H_
+
+#include <string.h>  // Provide access to size_t.
+
+#include <vector>
+
+#include "absl/types/optional.h"
+
+namespace webrtc {
+
+class Histogram {
+ public:
+  // Creates histogram with capacity `num_buckets` and `forget_factor` in Q15.
+  Histogram(size_t num_buckets,
+            int forget_factor,
+            absl::optional<double> start_forget_weight = absl::nullopt);
+
+  virtual ~Histogram();
+
+  // Resets the histogram to the default start distribution.
+  virtual void Reset();
+
+  // Add entry in bucket `index`.
+  virtual void Add(int index);
+
+  // Calculates the quantile at `probability` (in Q30) of the histogram
+  // distribution.
+  virtual int Quantile(int probability);
+
+  // Returns the number of buckets in the histogram.
+  virtual int NumBuckets() const;
+
+  // Returns the probability for each bucket in Q30.
+  const std::vector<int>& buckets() const { return buckets_; }
+
+  // Accessors only intended for testing purposes.
+  int base_forget_factor_for_testing() const { return base_forget_factor_; }
+  int forget_factor_for_testing() const { return forget_factor_; }
+  absl::optional<double> start_forget_weight_for_testing() const {
+    return start_forget_weight_;
+  }
+
+ private:
+  std::vector<int> buckets_;
+  int forget_factor_;  // Q15
+  const int base_forget_factor_;
+  int add_count_;
+  const absl::optional<double> start_forget_weight_;
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_CODING_NETEQ_HISTOGRAM_H_