Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/svg/SVGFEFloodElement.cpp

 /*
  * Copyright (C) 2004, 2005, 2007 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2007, 2008 Rob Buis <buis@kde.org>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 43 matching lines @@
         return flood->setFloodOpacity(style->svgStyle()->floodOpacity());
 
     ASSERT_NOT_REACHED();
     return false;
 }
 
 PassRefPtr<FilterEffect> SVGFEFloodElement::build(SVGFilterBuilder*, Filter* filter)
 {
     RenderObject* renderer = this->renderer();
     if (!renderer)
-        return 0;
+        return nullptr;
 
     ASSERT(renderer->style());
     const SVGRenderStyle* svgStyle = renderer->style()->svgStyle();
 
     Color color = svgStyle->floodColor();
     float opacity = svgStyle->floodOpacity();
 
     return FEFlood::create(filter, color, opacity);
 }
 
 }