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

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

 // Copyright (c) 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 "core/layout/HitTestCache.h"
 
+#include "platform/Histogram.h"
 #include "public/platform/Platform.h"
 
 namespace blink {
 
 bool HitTestCache::lookupCachedResult(HitTestResult& hitResult, uint64_t domTreeVersion)
 {
     bool result = false;
     HitHistogramMetric metric = HitHistogramMetric::MISS;
     if (hitResult.hitTestRequest().avoidCache()) {
         metric = HitHistogramMetric::MISS_EXPLICIT_AVOID;
     // For now we don't support rect based hit results.
     } else if (domTreeVersion == m_domTreeVersion && !hitResult.hitTestLocation().isRectBasedTest()) {
         for (const auto& cachedItem : m_items) {
             if (cachedItem.hitTestLocation().point() == hitResult.hitTestLocation().point()) {
                 if (hitResult.hitTestRequest().equalForCacheability(cachedItem.hitTestRequest())) {
                     metric = HitHistogramMetric::HIT_EXACT_MATCH;
                     result = true;
                     hitResult = cachedItem;
                     break;
                 }
                 metric = HitHistogramMetric::MISS_VALIDITY_RECT_MATCHES;
             }
         }
     }
-    Platform::current()->histogramEnumeration("Event.HitTest", static_cast<int>(metric), static_cast<int>(HitHistogramMetric::MAX_HIT_METRIC));
+    DEFINE_STATIC_LOCAL(EnumerationHistogram, hitTestHistogram, ("Event.HitTest", static_cast<int32_t>(HitHistogramMetric::MAX_HIT_METRIC)));
+    hitTestHistogram.count(static_cast<int32_t>(metric));
     return result;
 }
 
 void HitTestCache::addCachedResult(const HitTestResult& result, uint64_t domTreeVersion)
 {
     if (!result.isCacheable())
         return;
 
     // If the result was a hit test on an LayoutPart and the request allowed
     // querying of the layout part; then the part hasn't been loaded yet.
@@ skipping 21 matching lines @@
     m_updateIndex = 0;
     m_items.clear();
 }
 
 DEFINE_TRACE(HitTestCache)
 {
     visitor->trace(m_items);
 }
 
 } // namespace blink