Implement a Hit Test Cache.

Source/core/layout/line/InlineTextBox.cpp

 /*
  * (C) 1999 Lars Knoll (knoll@kde.org)
  * (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * 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.
  *
@@ skipping 303 matching lines @@
 {
     if (isLineBreak())
         return false;
 
     FloatPointWillBeLayoutPoint boxOrigin = locationIncludingFlipping();
     boxOrigin.moveBy(accumulatedOffset);
     FloatRectWillBeLayoutRect rect(boxOrigin, size());
     // 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;
 }
 
 bool InlineTextBox::getEmphasisMarkPosition(const ComputedStyle& style, TextEmphasisPosition& emphasisPosition) const
 {
     // This function returns true if there are text emphasis marks and they are suppressed by ruby text.
     if (style.textEmphasisMark() == TextEmphasisMarkNone)
         return false;
 
     emphasisPosition = style.textEmphasisPosition();
@@ skipping 213 matching lines @@
     printedCharacters = fprintf(stderr, "\t%s %p", obj.name(), &obj);
     const int layoutObjectCharacterOffset = 75;
     for (; printedCharacters < layoutObjectCharacterOffset; printedCharacters++)
         fputc(' ', stderr);
     fprintf(stderr, "(%d,%d) \"%s\"\n", start(), start() + len(), value.utf8().data());
 }
 
 #endif
 
 } // namespace blink