Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/svg/SVGFETurbulenceElement.cpp

 /*
  * Copyright (C) 2004, 2005, 2007 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006 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 144 matching lines @@
         primitiveAttributeChanged(attrName);
         return;
     }
 
     ASSERT_NOT_REACHED();
 }
 
 PassRefPtr<FilterEffect> SVGFETurbulenceElement::build(SVGFilterBuilder*, Filter* filter)
 {
     if (baseFrequencyX()->currentValue()->value() < 0 || baseFrequencyY()->currentValue()->value() < 0)
-        return 0;
+        return nullptr;
     return FETurbulence::create(filter, m_type->currentValue()->enumValue(), baseFrequencyX()->currentValue()->value(), baseFrequencyY()->currentValue()->value(), m_numOctaves->currentValue()->value(), m_seed->currentValue()->value(), m_stitchTiles->currentValue()->enumValue() == SVG_STITCHTYPE_STITCH);
 }
 
 }