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() {
+}
+
+base::TimeDelta PaintTimeCounter::GetPaintTimeOfRecentFrame(const size_t& n) const {

[reveman, 2013/01/16 22:48:04]

nit: line not <= 80 characters long.

+  DCHECK(n < ring_buffer_.BufferSize());
+
+  if (ring_buffer_.IsFilledIndex(n))
+    return ring_buffer_.ReadBuffer(n);
+
+  return base::TimeDelta();
+}
+
+void PaintTimeCounter::SavePaintTime(const base::TimeDelta& total_paint_time) {
+  base::TimeDelta paint_time = total_paint_time - last_total_paint_time_;
+
+  if (paint_time.InMillisecondsF() > 0)
+    ring_buffer_.SaveToBuffer(paint_time);
+
+  last_total_paint_time_ = total_paint_time;
+}
+
+void PaintTimeCounter::GetMinAndMaxPaintTimeInMilliseconds(double* min, double* max) const {

[reveman, 2013/01/16 22:48:04]

nit: line not <= 80 characters long.

+  *min = std::numeric_limits<double>::max();
+  *max = 0;
+
+  for (size_t i = 0; i < ring_buffer_.BufferSize(); i++) {

[egraether, 2013/01/16 19:31:56]

Loops in increasing direction because the iterator is now of type size_t.

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