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

cc/paint_time_counter.cc

Index: cc/paint_time_counter.cc
diff --git a/cc/paint_time_counter.cc b/cc/paint_time_counter.cc
new file mode 100644
index 0000000000000000000000000000000000000000..25b1bc677e9a7829cdf844a75d5c17588deeb5d4
--- /dev/null
+++ b/cc/paint_time_counter.cc
@@ -0,0 +1,56 @@
+// 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"
+
+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 {
+  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::GetMinAndMaxPaintTime(base::TimeDelta* min,
+                                             base::TimeDelta* max) const {
+  *min = base::TimeDelta::FromDays(1);
+  *max = base::TimeDelta();
+
+  for (size_t i = 0; i < ring_buffer_.BufferSize(); i++) {
+    if (ring_buffer_.IsFilledIndex(i)) {
+      base::TimeDelta paint_time = ring_buffer_.ReadBuffer(i);
+
+      if (paint_time < *min)
+        *min = paint_time;
+      if (paint_time > *max)
+        *max = paint_time;
+    }
+  }
+
+  if (*min > *max)
+    *min = *max;
+}
+
+}  // namespace cc