Add another uma metric for HitTesting validity.

Source/core/layout/HitTestResult.cpp

Index: Source/core/layout/HitTestResult.cpp
diff --git a/Source/core/layout/HitTestResult.cpp b/Source/core/layout/HitTestResult.cpp
index bba10d29df7bc7dfc008fb80cd292193efb530ab..7c02ae6f0c882d70558b13062727590e074bbc68 100644
--- a/Source/core/layout/HitTestResult.cpp
+++ b/Source/core/layout/HitTestResult.cpp
@@ -85,6 +85,7 @@ HitTestResult::HitTestResult(const HitTestRequest& otherRequest, const HitTestLo
 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)
@@ -110,6 +111,18 @@ HitTestResult& HitTestResult::operator=(const HitTestResult& 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)