cc: Reland "Add UMA stats for record and raster time."

cc/base/histograms.cc

+// Copyright 2015 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/base/histograms.h"
+
+#include <algorithm>
+#include <cmath>
+#include <limits>
+
+#include "base/numerics/safe_conversions.h"
+
+namespace cc {
+
+// Minimum elapsed time of 1us to limit weighting of fast calls.
+static const int64 kMinimumTimeMicroseconds = 1;
+
+ScopedUMAHistogramAreaTimerBase::ScopedUMAHistogramAreaTimerBase() : area_(0) {
+}
+
+ScopedUMAHistogramAreaTimerBase::~ScopedUMAHistogramAreaTimerBase() {
+}
+
+bool ScopedUMAHistogramAreaTimerBase::GetHistogramValues(
+    Sample* time_microseconds,
+    Sample* pixels_per_ms) const {
+  return GetHistogramValues(
+      timer_.Elapsed(), area_.ValueOrDefault(std::numeric_limits<int>::max()),
+      time_microseconds, pixels_per_ms);
+}
+
+// static
+bool ScopedUMAHistogramAreaTimerBase::GetHistogramValues(
+    base::TimeDelta elapsed,
+    int area,
+    Sample* time_microseconds,
+    Sample* pixels_per_ms) {
+  elapsed = std::max(
+      elapsed, base::TimeDelta::FromMicroseconds(kMinimumTimeMicroseconds));
+  double area_per_time = area / elapsed.InMillisecondsF();
+  // It is not clear how NaN can get here, but we've gotten crashes from
+  // saturated_cast. http://crbug.com/486214

[jamesr, 2015/05/27 19:34:19]

FYI in the past we've gotten unexpected results from floating point operations
on windows because some applications change the floating point control word (for
some threads): https://msdn.microsoft.com/en-us/library/e9b52ceh.aspx.  I think
norton (or one of the other bigger AVs) was doing this to Chrome in the past.
bug 486214 looks like it's not on windows but maybe somebody is mucking with the
floating point mode there.

+  if (std::isnan(area_per_time))
+    return false;
+  *time_microseconds = base::saturated_cast<Sample>(elapsed.InMicroseconds());
+  *pixels_per_ms = base::saturated_cast<Sample>(area_per_time);
+  return true;
+}
+
+}  // namespace cc