cc: add PaintTimeCounter to keep track of per frame paint time

cc/paint_time_counter.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/paint_time_counter.h"
+
+#include <limits>
+
+namespace cc {
+
+// static
+scoped_ptr<PaintTimeCounter> PaintTimeCounter::create() {
+  return make_scoped_ptr(new PaintTimeCounter());
+}
+
+PaintTimeCounter::PaintTimeCounter() {
+}
+
+double PaintTimeCounter::GetPaintTimeOfRecentFrame(int n) const {
+  DCHECK(n >= 0);
+  DCHECK(n < ring_buffer_.BufferSize());
+
+  if (ring_buffer_.IsFilledIndex(n))
+      return ring_buffer_.ReadBuffer(n);
+
+  return 0;
+}
+
+void PaintTimeCounter::SavePaintTime(double total_paint_time) {
+  double paint_time = total_paint_time - last_paint_time_;
+
+  if (paint_time > 0)
+    ring_buffer_.SaveToBuffer(paint_time);
+
+  last_paint_time_ = total_paint_time;
+}
+
+void PaintTimeCounter::GetMinAndMaxPaintTime(double& min, double& max) const {

[reveman, 2013/01/11 16:10:49]

chromium style doesn't allow using references for return values. just use
pointers here instead.

+  min = std::numeric_limits<double>::max();
+  max = 0;
+
+  for (int i = ring_buffer_.BufferSize() - 1; i > 0 && ring_buffer_.IsFilledIndex(i); --i) {

[reveman, 2013/01/11 16:10:49]

nit: lines should not be >= 80 characters.

[danakj, 2013/01/11 16:39:09]

s/>=/>/

"Each line of text in your code should be at most 80 characters long."

+    double paint_time = ring_buffer_.ReadBuffer(i);
+    min = std::min(paint_time, min);
+    max = std::max(paint_time, max);
+  }
+
+  if (min > max)
+    min = max;
+}
+
+}  // namespace cc