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

third_party/WebKit/Source/platform/Histogram.h

+// 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 {
+public:
+    CustomCountHistogram(const char* name, int32_t min, int32_t max, int32_t bucketCount);
+    void count(int32_t sample);
+
+protected:
+    CustomCountHistogram(base::HistogramBase*);

[esprehn, 2016/02/01 16:35:08]

explicit, note that even private and protected methods need explicit otherwise
you can inadvertently construct an object inside a member function. C++ is
crazy.

[dtapuska, 2016/02/01 16:43:31]

Done.

+
+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