Support caching histograms so that a lookup isn't done in each iteration.

third_party/WebKit/Source/platform/Histogram.h

Index: third_party/WebKit/Source/platform/Histogram.h
diff --git a/third_party/WebKit/Source/platform/Histogram.h b/third_party/WebKit/Source/platform/Histogram.h
new file mode 100644
index 0000000000000000000000000000000000000000..a782a28bfbeb63f34610c33a781afcfa91ca976e
--- /dev/null
+++ b/third_party/WebKit/Source/platform/Histogram.h
@@ -0,0 +1,46 @@
+// Copyright 2016 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 Histogram_h
+#define Histogram_h
+
+#include "platform/PlatformExport.h"
+#include <stdint.h>
+
+namespace base {
+class HistogramBase;
+};
+
+namespace blink {
+
+class PLATFORM_EXPORT CustomCountHistogram {

[bcwhite, 2016/02/01 20:06:18]

Why not have a HistogramBase equivalent rather than specific
CustomCountHistogram, EnumerationHistogram, etc.  That would make a more
extensible system for the future.

+public:
+    CustomCountHistogram(const char* name, int32_t min, int32_t max, int32_t bucketCount);
+    void count(int32_t sample);
+
+protected:
+    explicit CustomCountHistogram(base::HistogramBase*);
+
+private:
+    base::HistogramBase* m_histogram;
+};
+
+class PLATFORM_EXPORT EnumerationHistogram : public CustomCountHistogram {
+public:
+    EnumerationHistogram(const char* name, int32_t boundaryValue);
+};
+
+class PLATFORM_EXPORT SparseHistogram {
+public:
+    explicit SparseHistogram(const char* name);
+
+    void sample(int32_t sample);
+
+private:
+    base::HistogramBase* m_histogram;
+};
+
+} // namespace blink
+
+#endif // Histogram_h