cc: add RingBuffer class for timestamp storing in FrameRateCounter

cc/heads_up_display_layer_impl.cc

 // 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.
 
 #include "cc/heads_up_display_layer_impl.h"
 
 #include <limits>
 
 #include "base/stringprintf.h"
 #include "cc/debug_colors.h"
@@ skipping 196 matching lines @@
 
     drawFPSCounterText(canvas, paint, fpsCounter, textBounds);
     drawFPSCounterGraphAndHistogram(canvas, paint, fpsCounter, graphBounds, histogramBounds);
 
     return top + height;
 }
 
 void HeadsUpDisplayLayerImpl::drawFPSCounterText(SkCanvas* canvas, SkPaint& paint, FrameRateCounter* fpsCounter, SkRect bounds)
 {
     // Update FPS text - not every frame so text is readable
-    if (base::TimeDelta(fpsCounter->timeStampOfRecentFrame(0) - textUpdateTime).InSecondsF() > 0.25) {
+    base::TimeTicks now = base::TimeTicks::Now();
+    if (base::TimeDelta(now - textUpdateTime).InSecondsF() > 0.25) {
         m_averageFPS = fpsCounter->getAverageFPS();
-        textUpdateTime = fpsCounter->timeStampOfRecentFrame(0);
+        textUpdateTime = now;
     }
 
     // Draw FPS text.
     if (m_fontAtlas.get()) {
         std::string fpsText = base::StringPrintf("FPS:%5.1f", m_averageFPS);
         std::string minMaxText = base::StringPrintf("%.0f-%.0f", std::min( m_minFPS, m_maxFPS), m_maxFPS);
 
         int minMaxWidth = m_fontAtlas->textSize(minMaxText).width();
         gfx::Size textArea(bounds.width(), bounds.height());
 
@@ skipping 22 matching lines @@
     int x = 0;
     SkPath path;
 
     m_minFPS = std::numeric_limits<double>::max();
     m_maxFPS = 0;
 
     const int histogramSize = 20;
     double histogram[histogramSize] = {0};
     double maxBucketValue = 0;
 
-    for (int i = 1; i < fpsCounter->timeStampHistorySize() - 1; ++i) {
+    for (size_t i = 1; i < fpsCounter->timeStampHistorySize() - 1; ++i) {
         base::TimeDelta delta = fpsCounter->timeStampOfRecentFrame(i + 1) - fpsCounter->timeStampOfRecentFrame(i);
 
         // Skip this particular instantaneous frame rate if it is not likely to have been valid.
         if (!fpsCounter->isBadFrameInterval(delta)) {
 
             double fps = 1.0 / delta.InSecondsF();
 
             m_minFPS = std::min(fps, m_minFPS);
             m_maxFPS = std::max(fps, m_maxFPS);
 
@@ skipping 110 matching lines @@
 
     canvas->restore();
 }
 
 const char* HeadsUpDisplayLayerImpl::layerTypeAsString() const
 {
     return "HeadsUpDisplayLayer";
 }
 
 }  // namespace cc