improving UI of FPS counter

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"
 
 namespace cc {
 
 // This class maintains a history of timestamps, and provides functionality to
-// intelligently compute average frames per second (and standard deviation).
+// 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; }
-    void getAverageFPSAndStandardDeviation(double& averageFPS, double& standardDeviation) const;
+    double getAverageFPS() const;
     int timeStampHistorySize() const { return kTimeStampHistorySize; }
 
     // 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;
@@ skipping 26 matching lines @@
     base::TimeTicks m_timeStampHistory[kTimeStampHistorySize];
 
     int m_droppedFrameCount;
 
     DISALLOW_COPY_AND_ASSIGN(FrameRateCounter);
 };
 
 }  // namespace cc
 
 #endif  // CC_FRAME_RATE_COUNTER_H_