Support computing percentiles on a rolling window of samples

cc/scheduler/rolling_time_delta_history.h

Index: cc/scheduler/rolling_time_delta_history.h
diff --git a/cc/scheduler/rolling_time_delta_history.h b/cc/scheduler/rolling_time_delta_history.h
new file mode 100644
index 0000000000000000000000000000000000000000..947fb9855062b5b5d0c8c05af52b7cd8ef69d2c8
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+++ b/cc/scheduler/rolling_time_delta_history.h
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+// Copyright 2013 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 CC_SCHEDULER_ROLLING_TIME_DELTA_HISTORY_H_
+#define CC_SCHEDULER_ROLLING_TIME_DELTA_HISTORY_H_
+
+#include <deque>
+#include <set>
+
+#include "base/time.h"
+#include "cc/base/cc_export.h"
+
+namespace cc {
+
+// Stores a limited number of samples. When the maximum size is reached, each
+// insertion results in the deletion of the oldest remaining sample.
+class CC_EXPORT RollingTimeDeltaHistory {
+ public:
+  explicit RollingTimeDeltaHistory(size_t max_size);
+
+  ~RollingTimeDeltaHistory();
+
+  void InsertSample(base::TimeDelta time);
+
+  void Clear();
+
+  // Returns the smallest sample that is greater than or equal to the specified
+  // percent of samples. If there aren't any samples, returns base::TimeDelta().
+  base::TimeDelta Percentile(double percent) const;
+
+ private:
+  typedef std::multiset<base::TimeDelta> TimeDeltaMultiset;
+
+  TimeDeltaMultiset sample_set_;
+  std::deque<TimeDeltaMultiset::iterator> chronological_sample_deque_;
+  size_t max_size_;
+
+  DISALLOW_COPY_AND_ASSIGN(RollingTimeDeltaHistory);
+};
+
+}  // namespace cc
+
+#endif  // CC_SCHEDULER_ROLLING_TIME_DELTA_HISTORY_H_