Add another uma metric for HitTesting validity.

Source/core/layout/HitTestResult.cpp

 /*
  * Copyright (C) 2006, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies)
  *
  * 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 67 matching lines @@
     , m_hitTestRequest(otherRequest)
     , m_cacheable(true)
     , m_pointInInnerNodeFrame(m_hitTestLocation.point())
     , m_isOverWidget(false)
 {
 }
 
 HitTestResult::HitTestResult(const HitTestResult& other)
     : m_hitTestLocation(other.m_hitTestLocation)
     , m_hitTestRequest(other.m_hitTestRequest)
+    , m_cacheable(other.m_cacheable)

[Rick Byers, 2015/06/25 20:58:27]

was this an unrelated bug?

[dtapuska, 2015/06/25 21:01:33]

Yes it was; this constructor isn't used in the code path that would be an issue
although it does need to be fixed.

     , m_innerNode(other.innerNode())
     , m_innerPossiblyPseudoNode(other.m_innerPossiblyPseudoNode)
     , m_pointInInnerNodeFrame(other.m_pointInInnerNodeFrame)
     , m_localPoint(other.localPoint())
     , m_innerURLElement(other.URLElement())
     , m_scrollbar(other.scrollbar())
     , m_isOverWidget(other.isOverWidget())
 {
     // Only copy the NodeSet in case of list hit test.
     m_listBasedTestResult = adoptPtrWillBeNoop(other.m_listBasedTestResult ? new NodeSet(*other.m_listBasedTestResult) : 0);
 }
 
 HitTestResult::~HitTestResult()
 {
 }
 
 HitTestResult& HitTestResult::operator=(const HitTestResult& other)
 {
     m_hitTestLocation = other.m_hitTestLocation;
     m_hitTestRequest = other.m_hitTestRequest;
     populateFromCachedResult(other);
 
     return *this;
 }
 
+unsigned HitTestResult::equalityScore(const HitTestResult& other) const
+{
+    return (m_hitTestRequest.equalForCacheability(other.m_hitTestRequest) << 7)
+        | ((m_innerNode == other.innerNode()) << 6)
+        | ((m_innerPossiblyPseudoNode == other.innerPossiblyPseudoNode()) << 5)
+        | ((m_pointInInnerNodeFrame == other.m_pointInInnerNodeFrame) << 4)
+        | ((m_localPoint == other.localPoint()) << 3)
+        | ((m_innerURLElement == other.URLElement()) << 2)
+        | ((m_scrollbar == other.scrollbar()) << 1)
+        | (m_isOverWidget == other.isOverWidget());
+}
+
 bool HitTestResult::equalForCacheability(const HitTestResult& other) const
 {
     return m_hitTestRequest.equalForCacheability(other.m_hitTestRequest)
         && m_innerNode == other.innerNode()
         && m_innerPossiblyPseudoNode == other.innerPossiblyPseudoNode()
         && m_pointInInnerNodeFrame == other.m_pointInInnerNodeFrame
         && m_localPoint == other.localPoint()
         && m_innerURLElement == other.URLElement()
         && m_scrollbar == other.scrollbar()
         && m_isOverWidget == other.isOverWidget();
@@ skipping 416 matching lines @@
     else if (isHTMLMapElement(m_innerNode))
         imageMapImageElement = toHTMLMapElement(m_innerNode)->imageElement();
 
     if (!imageMapImageElement)
         return m_innerNode.get();
 
     return imageMapImageElement;
 }
 
 } // namespace blink