Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/html/canvas/WebGLRenderingContext.h

 /*
  * Copyright (C) 2009 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 597 matching lines @@
         TypedExtensionTracker(RefPtr<T>& extensionField, ExtensionFlags flags, const char* const* prefixes)
             : ExtensionTracker(flags, prefixes)
             , m_extensionField(extensionField)
         {
         }
 
         virtual ~TypedExtensionTracker()
         {
             if (m_extensionField) {
                 m_extensionField->lose(true);
-                m_extensionField = 0;
+                m_extensionField = nullptr;
             }
         }
 
         virtual PassRefPtr<WebGLExtension> getExtension(WebGLRenderingContext* context) const OVERRIDE
         {
             if (!m_extensionField)
                 m_extensionField = T::create(context);
 
             return m_extensionField;
         }
 
         virtual bool supported(WebGLRenderingContext* context) const OVERRIDE
         {
             return T::supported(context);
         }
 
         virtual const char* extensionName() const OVERRIDE
         {
             return T::extensionName();
         }
 
         virtual void loseExtension() OVERRIDE
         {
             if (m_extensionField) {
                 m_extensionField->lose(false);
                 if (m_extensionField->isLost())
-                    m_extensionField = 0;
+                    m_extensionField = nullptr;
             }
         }
 
     private:
         RefPtr<T>& m_extensionField;
     };
 
     Vector<ExtensionTracker*> m_extensions;
 
     template <typename T>
@@ skipping 261 matching lines @@
     // If the vector is empty, return the maximum allowed active context number.
     static size_t oldestContextIndex();
     static IntSize oldestContextSize();
 };
 
 DEFINE_TYPE_CASTS(WebGLRenderingContext, CanvasRenderingContext, context, context->is3d(), context.is3d());
 
 } // namespace WebCore
 
 #endif