Implement a Hit Test Cache.

Source/core/layout/line/InlineTextBox.cpp

Index: Source/core/layout/line/InlineTextBox.cpp
diff --git a/Source/core/layout/line/InlineTextBox.cpp b/Source/core/layout/line/InlineTextBox.cpp
index 3ff2c6096ef752600b81173ddb5bfaa19946e3b0..d975dd0f673c1bc589969adea0945bf1631c12f5 100644
--- a/Source/core/layout/line/InlineTextBox.cpp
+++ b/Source/core/layout/line/InlineTextBox.cpp
@@ -321,10 +321,11 @@ bool InlineTextBox::nodeAtPoint(HitTestResult& result, const HitTestLocation& lo
     // FIXME: both calls to rawValue() below is temporary and should be removed once the transition
     // to LayoutUnit-based types is complete (crbug.com/321237)
     if (m_truncation != cFullTruncation && visibleToHitTestRequest(result.hitTestRequest()) && locationInContainer.intersects(rect.rawValue())) {
-        layoutObject().updateHitTestResult(result, flipForWritingMode(locationInContainer.point() - toLayoutSize(accumulatedOffset)));
+        layoutObject().updateHitTestResult(result, flipForWritingMode(locationInContainer.point() - toLayoutSize(accumulatedOffset)), rect);
         if (!result.addNodeToListBasedTestResult(layoutObject().node(), locationInContainer, rect.rawValue()))
             return true;
     }
+    result.shrinkValidityRect(rect);
     return false;
 }