Introduce cadence based VideoRendererAlgorithm.

media/base/moving_average.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef MEDIA_BASE_MOVING_AVERAGE_H_
+#define MEDIA_BASE_MOVING_AVERAGE_H_
+
+#include <vector>
+
+#include "base/time/time.h"
+#include "media/base/media_export.h"
+
+namespace media {
+
+// Simple class for calculating a moving average of fixed size.
+class MEDIA_EXPORT MovingAverage {
+ public:
+  // Creates a MovingAverage instance with space for |depth| samples.
+  explicit MovingAverage(size_t depth);
+  ~MovingAverage();
+
+  // Adds a new sample to the average; replaces the oldest sample if |depth_|
+  // has been exceeded.  Updates |total_| to the new sum of values.
+  void AddSample(base::TimeDelta sample);
+
+  // Returns the current average of all held samples.
+  base::TimeDelta Average() const;
+
+  // Resets the state of the class to its initial post-construction state.
+  void Reset();
+
+ private:
+  // Maximum number of elements allowed in the average.
+  const size_t depth_;
+
+  // Number of elements seen thus far.
+  size_t count_;
+
+  std::vector<base::TimeDelta> samples_;
+  base::TimeDelta total_;
+
+  DISALLOW_COPY_AND_ASSIGN(MovingAverage);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_MOVING_AVERAGE_H_