Add another uma metric for HitTesting validity.

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 "config.h"
 #include "core/layout/HitTestCache.h"
 
 #include "public/platform/Platform.h"
 
 namespace blink {
@@ skipping 20 matching lines @@
     }
     Platform::current()->histogramEnumeration("Event.HitTest", static_cast<int>(metric), static_cast<int>(HitHistogramMetric::MAX_HIT_METRIC));
     return result;
 }
 
 void HitTestCache::verifyCachedResult(const HitTestResult& expected, const HitTestResult& actual)
 {
     ValidityHistogramMetric metric;
     if (!actual.equalForCacheability(expected)) {
         metric = expected.hitTestLocation().isRectBasedTest() ? ValidityHistogramMetric::INCORRECT_RECT_BASED_EXACT_MATCH : ValidityHistogramMetric::INCORRECT_POINT_EXACT_MATCH;
+        Platform::current()->histogramSparse("Event.HitTestValidityScore", static_cast<int>(actual.equalityScore(expected)));
 
         // ASSERT that the cache hit is the same as the actual result.
         ASSERT_NOT_REACHED();
     } else {
         metric = ValidityHistogramMetric::VALID_EXACT_MATCH;
     }
     Platform::current()->histogramEnumeration("Event.HitTestValidity", static_cast<int>(metric), static_cast<int>(ValidityHistogramMetric::MAX_VALIDITY_METRIC));
 }
 
 void HitTestCache::addCachedResult(const HitTestResult& result, uint64_t domTreeVersion)
@@ skipping 27 matching lines @@
     m_updateIndex = 0;
     m_items.clear();
 }
 
 DEFINE_TRACE(HitTestCache)
 {
     visitor->trace(m_items);
 }
 
 } // namespace blink