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 190 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();

[egraether, 2013/01/10 02:32:09]

This should just use the current timestamp, which is easier to understand.

+    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 153 matching lines @@
 
     canvas->restore();
 }
 
 const char* HeadsUpDisplayLayerImpl::layerTypeAsString() const
 {
     return "HeadsUpDisplayLayer";
 }
 
 }  // namespace cc