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

cc/base/histograms.h

Index: cc/base/histograms.h
diff --git a/cc/base/histograms.h b/cc/base/histograms.h
new file mode 100644
index 0000000000000000000000000000000000000000..0c8a2bc8532e627a3d9c03fedafdd0248fb8c502
--- /dev/null
+++ b/cc/base/histograms.h
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+// 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.
+
+#ifndef CC_BASE_HISTOGRAMS_H_
+#define CC_BASE_HISTOGRAMS_H_
+
+#include "base/compiler_specific.h"
+#include "base/metrics/histogram_base.h"
+#include "base/metrics/histogram_macros.h"
+#include "base/numerics/safe_math.h"
+#include "base/time/time.h"
+#include "base/timer/elapsed_timer.h"
+#include "cc/base/cc_export.h"
+
+namespace cc {
+
+// Emits UMA histogram trackers for time spent as well as area (in pixels)
+// processed per unit time. Time is measured in microseconds, and work in
+// pixels per millisecond.
+//
+// Usage:
+//   // Outside of a method, perhaps in a namespace.
+//   DEFINE_SCOPED_UMA_HISTOGRAM_AREA_TIMER(ScopedReticulateSplinesTimer,
+//                                          "ReticulateSplinesUs",
+//                                          "ReticulateSplinesPixelsPerMs");
+//
+//   // Inside a method.
+//   ScopedReticulateSplinesTimer timer;
+//   timer.AddArea(some_rect.size().GetArea());
+#define DEFINE_SCOPED_UMA_HISTOGRAM_AREA_TIMER(class_name, time_histogram, \
+                                               area_histogram)             \
+  class class_name : public ::cc::ScopedUMAHistogramAreaTimerBase {        \
+   public:                                                                 \
+    ~class_name();                                                         \
+  };                                                                       \
+  class_name::~class_name() {                                              \
+    Sample time_sample;                                                    \
+    Sample area_sample;                                                    \
+    if (GetHistogramValues(&time_sample, &area_sample)) {                  \
+      UMA_HISTOGRAM_COUNTS(time_histogram, time_sample);                   \
+      UMA_HISTOGRAM_COUNTS(area_histogram, area_sample);                   \
+    }                                                                      \
+  }
+
+class CC_EXPORT ScopedUMAHistogramAreaTimerBase {
+ public:
+  void AddArea(int area) { area_ += area; }
+  void SetArea(int area) { area_ = area; }
+
+ protected:
+  using Sample = base::HistogramBase::Sample;
+
+  ScopedUMAHistogramAreaTimerBase();
+  ~ScopedUMAHistogramAreaTimerBase();
+
+  // Returns true if histograms should be recorded (i.e. values are valid).
+  bool GetHistogramValues(Sample* time_microseconds,
+                          Sample* pixels_per_ms) const;
+
+ private:
+  static bool GetHistogramValues(base::TimeDelta elapsed,
+                                 int area,
+                                 Sample* time_microseconds,
+                                 Sample* pixels_per_ms);
+
+  base::ElapsedTimer timer_;
+  base::CheckedNumeric<int> area_;
+
+  friend class ScopedUMAHistogramAreaTimerBaseTest;
+  DISALLOW_COPY_AND_ASSIGN(ScopedUMAHistogramAreaTimerBase);
+};
+
+}  // namespace cc
+
+#endif  // CC_BASE_HISTOGRAMS_H_