Implement a Hit Test Cache.

Source/platform/LayoutUnit.h

 /*
  * Copyright (c) 2012, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 152 matching lines @@
     }
 
     bool mightBeSaturated() const
     {
         return rawValue() == std::numeric_limits<int>::max()
             || rawValue() == std::numeric_limits<int>::min();
     }
 
     static float epsilon() { return 1.0f / kFixedPointDenominator; }
 
+    static const LayoutUnit epsilonUnit()
+    {
+        LayoutUnit m;
+        m.m_value = 1;
+        return m;
+    }
+
     static const LayoutUnit max()
     {
         LayoutUnit m;
         m.m_value = std::numeric_limits<int>::max();
         return m;
     }
     static const LayoutUnit min()
     {
         LayoutUnit m;
         m.m_value = std::numeric_limits<int>::min();
@@ skipping 606 matching lines @@
     if (value >= max)
         return max;
     if (value <= min)
         return min;
     return value;
 }
 
 } // namespace blink
 
 #endif // LayoutUnit_h