Introduce cadence based VideoRendererAlgorithm.

media/base/moving_average.cc

+// 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.
+
+#include "media/base/moving_average.h"
+
+#include <algorithm>
+
+namespace media {
+
+MovingAverage::MovingAverage(size_t depth)
+    : depth_(depth), count_(0), samples_(new base::TimeDelta[depth]) {
+}
+
+MovingAverage::~MovingAverage() {
+}
+
+void MovingAverage::AddSample(base::TimeDelta sample) {
+  if (count_ < depth_) {
+    samples_[count_++] = sample;
+    total_ += sample;
+    return;
+  }
+
+  base::TimeDelta& oldest = samples_[count_++ % depth_];
+  total_ += sample - oldest;
+  oldest = sample;
+}
+
+base::TimeDelta MovingAverage::Average() const {
+  DCHECK_GT(count_, 0u);
+  return total_ / std::min(depth_, count_);
+}
+
+void MovingAverage::Reset() {
+  count_ = 0;
+  total_ = base::TimeDelta();
+}
+
+}  // namespace media