Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/wtf/NullPtr.h

 /*
 
 Copyright (C) 2010 Apple 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:
 1.  Redistributions of source code must retain the above copyright
     notice, this list of conditions and the following disclaimer.
 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 39 matching lines @@
 class nullptr_t { };
 }
 extern std::nullptr_t nullptr;
 
 #endif
 
 #if COMPILER_SUPPORTS(CXX_DELETED_FUNCTIONS)
 #define WTF_DISALLOW_CONSTRUCTION_FROM_ZERO(ClassName) \
     private: \
         ClassName(int) = delete
+#define WTF_DISALLOW_ZERO_ASSIGNMENT(ClassName) \
+    private: \
+        ClassName& operator=(int) = delete
 #else
 #define WTF_DISALLOW_CONSTRUCTION_FROM_ZERO(ClassName) \
     private: \
         ClassName(int)
+#define WTF_DISALLOW_ZERO_ASSIGNMENT(ClassName) \
+    private: \
+        ClassName& operator=(int)
 #endif
 
 #endif