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

third_party/WebKit/Source/core/layout/LayoutView.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 48 matching lines @@
 public:
     HitTestLatencyRecorder(bool allowsChildFrameContent)
         : m_start(WTF::monotonicallyIncreasingTime())
         , m_allowsChildFrameContent(allowsChildFrameContent)
     {
     }
 
     ~HitTestLatencyRecorder()
     {
         int duration = static_cast<int>((WTF::monotonicallyIncreasingTime() - m_start) * 1000000);
-        Platform::current()->histogramCustomCounts(m_allowsChildFrameContent ? "Event.Latency.HitTestRecursive" : "Event.Latency.HitTest", duration, 0, 10000000, 100);
+        if (m_allowsChildFrameContent) {
+            static Platform::HistogramCacheSlot histogramCache = 0;
+            Platform::current()->histogramCustomCounts("Event.Latency.HitTestRecursive", duration, 0, 10000000, 100, &histogramCache);

[esprehn, 2016/01/29 23:05:40]

DEFINE_STATIC_LOCAL(Histogram, hitTestLatency,
("Event.Latency.HitTestRecursive", 0, 10000000, 100));

hitTestLatency.record(duration);

+        } else {
+            static Platform::HistogramCacheSlot histogramCache = 0;
+            Platform::current()->histogramCustomCounts("Event.Latency.HitTest", duration, 0, 10000000, 100, &histogramCache);
+        }
     }
 
 private:
     double m_start;
     bool m_allowsChildFrameContent;
 };
 
 } // namespace
 
 LayoutView::LayoutView(Document* document)
@@ skipping 908 matching lines @@
 }
 
 void LayoutView::sendMediaPositionChangeNotifications(const IntRect& visibleRect)
 {
     for (auto& media : m_mediaForPositionNotification) {
         media->notifyPositionMayHaveChanged(visibleRect);
     }
 }
 
 } // namespace blink