Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/rendering/RenderImageResourceStyleImage.cpp

 /*
  * Copyright (C) 1999 Lars Knoll <knoll@kde.org>
  * Copyright (C) 1999 Antti Koivisto <koivisto@kde.org>
  * Copyright (C) 2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2006 Allan Sandfeld Jensen <kde@carewolf.com>
  * Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
  * Copyright (C) 2003, 2004, 2005, 2006, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) 2010 Patrick Gansterer <paroga@paroga.com>
  *
@@ skipping 47 matching lines @@
 {
     ASSERT(m_renderer);
     m_styleImage->removeClient(m_renderer);
     m_cachedImage = 0;
 }
 
 PassRefPtr<Image> RenderImageResourceStyleImage::image(int width, int height) const
 {
     // Generated content may trigger calls to image() while we're still pending, don't assert but gracefully exit.
     if (m_styleImage->isPendingImage())
-        return 0;
+        return nullptr;
     return m_styleImage->image(m_renderer, IntSize(width, height));
 }
 
 void RenderImageResourceStyleImage::setContainerSizeForRenderer(const IntSize& size)
 {
     ASSERT(m_renderer);
     m_styleImage->setContainerSizeForRenderer(m_renderer, size, m_renderer->style()->effectiveZoom());
 }
 
 } // namespace WebCore