Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/dom/shadow/ElementShadow.cpp

 /*
  * 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.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 371 matching lines @@
         shadow->setNeedsSelectFeatureSet();
     }
     setNeedsDistributionRecalc();
 }
 
 void ElementShadow::clearDistribution()
 {
     m_nodeToInsertionPoints.clear();
 
     for (ShadowRoot* root = youngestShadowRoot(); root; root = root->olderShadowRoot())
-        root->setShadowInsertionPointOfYoungerShadowRoot(0);
+        root->setShadowInsertionPointOfYoungerShadowRoot(nullptr);
 }
 
 } // namespace