Implement a Hit Test Cache.

Source/core/layout/LayoutImage.cpp

Index: Source/core/layout/LayoutImage.cpp
diff --git a/Source/core/layout/LayoutImage.cpp b/Source/core/layout/LayoutImage.cpp
index 44afdeacb42ce446a9397cb354e6afbf7785bcdc..eb80587120b242c0821d10eb2a9587ec5324ce5b 100644
--- a/Source/core/layout/LayoutImage.cpp
+++ b/Source/core/layout/LayoutImage.cpp
@@ -274,12 +274,15 @@ HTMLMapElement* LayoutImage::imageMap() const
 bool LayoutImage::nodeAtPoint(HitTestResult& result, const HitTestLocation& locationInContainer, const LayoutPoint& accumulatedOffset, HitTestAction hitTestAction)
 {
     HitTestResult tempResult(result.hitTestRequest(), result.hitTestLocation());
+    tempResult.setValidityRect(result.validityRect());
     bool inside = LayoutReplaced::nodeAtPoint(tempResult, locationInContainer, accumulatedOffset, hitTestAction);
 
     if (!inside && result.hitTestRequest().listBased())
         result.append(tempResult);
     if (inside)
         result = tempResult;
+    else
+        result.setValidityRect(tempResult.validityRect());
     return inside;
 }