Initial import attempt, just to play with. Many things disabled/removed

ui/cc/cc/CCFrameRateCounter.cpp

Index: ui/cc/cc/CCFrameRateCounter.cpp
diff --git a/ui/cc/cc/CCFrameRateCounter.cpp b/ui/cc/cc/CCFrameRateCounter.cpp
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index 0000000000000000000000000000000000000000..d6dff06ab0cb185074421742a11e846506e23ee9
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+++ b/ui/cc/cc/CCFrameRateCounter.cpp
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+/*
+ * Copyright (C) 2012 Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1.  Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ * 2.  Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+
+#if USE(ACCELERATED_COMPOSITING)
+#include "CCFrameRateCounter.h"
+
+#include "CCProxy.h"
+#include <wtf/CurrentTime.h>
+
+namespace WebCore {
+
+const double CCFrameRateCounter::kFrameTooFast = 1.0 / 70.0; // measured in seconds
+const double CCFrameRateCounter::kFrameTooSlow = 1.0 / 12.0;
+
+// safeMod works on -1, returning m-1 in that case.
+static inline int safeMod(int number, int modulus)
+{
+    return (number + modulus) % modulus;
+}
+
+inline int CCFrameRateCounter::frameIndex(int frame) const
+{
+    return safeMod(frame, kTimeStampHistorySize);
+}
+
+CCFrameRateCounter::CCFrameRateCounter()
+    : m_currentFrameNumber(1)
+{
+    m_timeStampHistory[0] = currentTime();
+    m_timeStampHistory[1] = m_timeStampHistory[0];
+    for (int i = 2; i < kTimeStampHistorySize; i++)
+        m_timeStampHistory[i] = 0;
+}
+
+void CCFrameRateCounter::markBeginningOfFrame(double timestamp)
+{
+    m_timeStampHistory[frameIndex(m_currentFrameNumber)] = timestamp;
+}
+
+void CCFrameRateCounter::markEndOfFrame()
+{
+    m_currentFrameNumber += 1;
+}
+
+bool CCFrameRateCounter::isBadFrameInterval(double intervalBetweenConsecutiveFrames) const
+{
+    bool schedulerAllowsDoubleFrames = !CCProxy::hasImplThread();
+    bool intervalTooFast = schedulerAllowsDoubleFrames && intervalBetweenConsecutiveFrames < kFrameTooFast;
+    bool intervalTooSlow = intervalBetweenConsecutiveFrames > kFrameTooSlow;
+    return intervalTooFast || intervalTooSlow;
+}
+
+bool CCFrameRateCounter::isBadFrame(int frameNumber) const
+{
+    double delta = m_timeStampHistory[frameIndex(frameNumber)] -
+            m_timeStampHistory[frameIndex(frameNumber - 1)];
+    return isBadFrameInterval(delta);
+}
+
+void CCFrameRateCounter::getAverageFPSAndStandardDeviation(double& averageFPS, double& standardDeviation) const
+{
+    int frame = m_currentFrameNumber - 1;
+    averageFPS = 0;
+    int averageFPSCount = 0;
+    double fpsVarianceNumerator = 0;
+
+    // Walk backwards through the samples looking for a run of good frame
+    // timings from which to compute the mean and standard deviation.
+    //
+    // Slow frames occur just because the user is inactive, and should be
+    // ignored. Fast frames are ignored if the scheduler is in single-thread
+    // mode in order to represent the true frame rate in spite of the fact that
+    // the first few swapbuffers happen instantly which skews the statistics
+    // too much for short lived animations.
+    //
+    // isBadFrame encapsulates the frame too slow/frame too fast logic.
+    while (1) {
+        if (!isBadFrame(frame)) {
+            averageFPSCount++;
+            double secForLastFrame = m_timeStampHistory[frameIndex(frame)] -
+                                     m_timeStampHistory[frameIndex(frame - 1)];
+            double x = 1.0 / secForLastFrame;
+            double deltaFromAverage = x - averageFPS;
+            // Change with caution - numerics. http://en.wikipedia.org/wiki/Standard_deviation
+            averageFPS = averageFPS + deltaFromAverage / averageFPSCount;
+            fpsVarianceNumerator = fpsVarianceNumerator + deltaFromAverage * (x - averageFPS);
+        }
+        if (averageFPSCount && isBadFrame(frame)) {
+            // We've gathered a run of good samples, so stop.
+            break;
+        }
+        --frame;
+        if (frameIndex(frame) == frameIndex(m_currentFrameNumber) || frame < 0) {
+            // We've gone through all available historical data, so stop.
+            break;
+        }
+    }
+
+    standardDeviation = sqrt(fpsVarianceNumerator / averageFPSCount);
+}
+
+double CCFrameRateCounter::timeStampOfRecentFrame(int n)
+{
+    ASSERT(n >= 0 && n < kTimeStampHistorySize);
+    int desiredIndex = (frameIndex(m_currentFrameNumber) + n) % kTimeStampHistorySize;
+    return m_timeStampHistory[desiredIndex];
+}
+
+} // namespace WebCore
+
+#endif // USE(ACCELERATED_COMPOSITING)