Implement a Hit Test Cache.

Source/core/layout/LayoutTextFragment.cpp

Index: Source/core/layout/LayoutTextFragment.cpp
diff --git a/Source/core/layout/LayoutTextFragment.cpp b/Source/core/layout/LayoutTextFragment.cpp
index 0850f7cd4fc81102612d5370293963215aec4903..c4aa36c8e8b98786c420981f63ccc6e7a5449b34 100644
--- a/Source/core/layout/LayoutTextFragment.cpp
+++ b/Source/core/layout/LayoutTextFragment.cpp
@@ -155,12 +155,12 @@ Text* LayoutTextFragment::associatedTextNode() const
     return (node && node->isTextNode()) ? toText(node) : nullptr;
 }
 
-void LayoutTextFragment::updateHitTestResult(HitTestResult& result, const LayoutPoint& point)
+void LayoutTextFragment::updateHitTestResult(HitTestResult& result, const LayoutPoint& point, const LayoutRect& rect)
 {
     if (result.innerNode())
         return;
 
-    LayoutObject::updateHitTestResult(result, point);
+    LayoutObject::updateHitTestResult(result, point, rect);
 
     // If we aren't part of a first-letter element, or if we
     // are part of first-letter but we're the remaining text then return.