cc: add RingBuffer class for timestamp storing in FrameRateCounter

cc/heads_up_display_layer_impl.cc

Index: cc/heads_up_display_layer_impl.cc
diff --git a/cc/heads_up_display_layer_impl.cc b/cc/heads_up_display_layer_impl.cc
index 177f349558981a9a7d302b80ad99d555fb2c584b..07d8e2d8c324b680101dcd91964e87363e148e85 100644
--- a/cc/heads_up_display_layer_impl.cc
+++ b/cc/heads_up_display_layer_impl.cc
@@ -178,7 +178,7 @@ int HeadsUpDisplayLayerImpl::drawFPSCounter(SkCanvas* canvas, FrameRateCounter*
 
     const int fontHeight = m_fontAtlas.get() ? m_fontAtlas->fontHeight() : 0;
 
-    const int graphWidth = fpsCounter->timeStampHistorySize() - 3;
+    const int graphWidth = fpsCounter->bufferSize() - 3;
     const int graphHeight = 40;
 
     const int histogramWidth = 37;
@@ -208,9 +208,9 @@ int HeadsUpDisplayLayerImpl::drawFPSCounter(SkCanvas* canvas, FrameRateCounter*
 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) {
+    if (base::TimeDelta(fpsCounter->readBuffer(0) - textUpdateTime).InSecondsF() > 0.25) {

[shawnsingh, 2013/01/09 20:55:09]

Personally, as I'm reading the code here, I would like a more intuitive,
meaningful name than "readBuffer".  I would like to see something that makes it
clear that we're accessing a recent timestamp that has been stored in the
fpsCounter.  Perhaps we could keep the timeStampOfRecentFrame() and
timeStampHistorySize() functions the same, and just make them trivial inlined
wrappers to use the ring buffer?

That may also make it possible for fpsCounter to own an instance of RingBuffer,
rather than to inherit it.  I don't feel too strongly either way, but in my
opinion, the owning concept makes more sense - i.e.  "fpsCounter uses a
RingBuffer" , not  "fpsCounter is a RingBuffer".

         m_averageFPS = fpsCounter->getAverageFPS();
-        textUpdateTime = fpsCounter->timeStampOfRecentFrame(0);
+        textUpdateTime = fpsCounter->readBuffer(0);
     }
 
     // Draw FPS text.
@@ -253,8 +253,8 @@ void HeadsUpDisplayLayerImpl::drawFPSCounterGraphAndHistogram(SkCanvas* canvas,
     double histogram[histogramSize] = {0};
     double maxBucketValue = 0;
 
-    for (int i = 1; i < fpsCounter->timeStampHistorySize() - 1; ++i) {
-        base::TimeDelta delta = fpsCounter->timeStampOfRecentFrame(i + 1) - fpsCounter->timeStampOfRecentFrame(i);
+    for (int i = 1; i < fpsCounter->bufferSize() - 1; ++i) {
+        base::TimeDelta delta = fpsCounter->readBuffer(i + 1) - fpsCounter->readBuffer(i);
 
         // Skip this particular instantaneous frame rate if it is not likely to have been valid.
         if (!fpsCounter->isBadFrameInterval(delta)) {