cc: add RingBuffer class for timestamp storing in FrameRateCounter

cc/frame_rate_counter.h

 // Copyright 2012 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_FRAME_RATE_COUNTER_H_
 #define CC_FRAME_RATE_COUNTER_H_
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/time.h"
+#include "cc/ring_buffer.h"
 
 namespace cc {
 
 // This class maintains a history of timestamps, and provides functionality to
 // intelligently compute average frames per second.
 class FrameRateCounter {
 public:
     static scoped_ptr<FrameRateCounter> create(bool hasImplThread);
 
-    void markBeginningOfFrame(base::TimeTicks timestamp);
-    void markEndOfFrame();
-    int currentFrameNumber() const { return m_currentFrameNumber; }
-    double getAverageFPS() const;
-    int timeStampHistorySize() const { return kTimeStampHistorySize; }
+    int currentFrameNumber() const { return m_ringBuffer.CurrentIndex(); }
+    int droppedFrameCount() const { return m_droppedFrameCount; }
+    int timeStampHistorySize() const { return m_ringBuffer.BufferSize(); }
+
+    void saveTimeStamp(base::TimeTicks timestamp);
 
     // n = 0 returns the oldest frame retained in the history,
     // while n = timeStampHistorySize() - 1 returns the timestamp most recent frame.
-    // FIXME: Returns most recent timestamp for n = 0 when called between markBeginningOfFrame and markEndOfFrame calls.
     base::TimeTicks timeStampOfRecentFrame(int n) const;
 
     // This is a heuristic that can be used to ignore frames in a reasonable way. Returns
     // true if the given frame interval is too fast or too slow, based on constant thresholds.
     bool isBadFrameInterval(base::TimeDelta intervalBetweenConsecutiveFrames) const;
 
-    int droppedFrameCount() const { return m_droppedFrameCount; }
+    void getMinAndMaxFPS(double& minFPS, double& maxFPS) const;
+    double getAverageFPS() const;
 
 private:
     explicit FrameRateCounter(bool hasImplThread);
 
-    base::TimeDelta frameInterval(int frameNumber) const;
-    int frameIndex(int frameNumber) const;
-    bool isBadFrame(int frameNumber) const;
+    base::TimeDelta recentFrameInterval(int n) const;
 
     // Two thresholds (measured in seconds) that describe what is considered to be a "no-op frame" that should not be counted.
     // - if the frame is too fast, then given our compositor implementation, the frame probably was a no-op and did not draw.
     // - if the frame is too slow, then there is probably not animating content, so we should not pollute the average.
     static const double kFrameTooFast;
     static const double kFrameTooSlow;
 
     // If a frame takes longer than this threshold (measured in seconds) then we
     // (naively) assume that it missed a screen refresh; that is, we dropped a frame.
     // FIXME: Determine this threshold based on monitor refresh rate, crbug.com/138642.
     static const double kDroppedFrameTime;
 
-    static const int kTimeStampHistorySize = 130;
+    RingBuffer<base::TimeTicks, 130> m_ringBuffer;
 
     bool m_hasImplThread;
-
-    int m_currentFrameNumber;
-    base::TimeTicks m_timeStampHistory[kTimeStampHistorySize];
-
     int m_droppedFrameCount;
 
     DISALLOW_COPY_AND_ASSIGN(FrameRateCounter);
 };
 
 }  // namespace cc
 
 #endif  // CC_FRAME_RATE_COUNTER_H_