Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/svg/SVGFEGaussianBlurElement.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 93 matching lines @@
     }
 
     ASSERT_NOT_REACHED();
 }
 
 PassRefPtr<FilterEffect> SVGFEGaussianBlurElement::build(SVGFilterBuilder* filterBuilder, Filter* filter)
 {
     FilterEffect* input1 = filterBuilder->getEffectById(AtomicString(m_in1->currentValue()->value()));
 
     if (!input1)
-        return 0;
+        return nullptr;
 
     if (stdDeviationX()->currentValue()->value() < 0 || stdDeviationY()->currentValue()->value() < 0)
-        return 0;
+        return nullptr;
 
     RefPtr<FilterEffect> effect = FEGaussianBlur::create(filter, stdDeviationX()->currentValue()->value(), stdDeviationY()->currentValue()->value());
     effect->inputEffects().append(input1);
     return effect.release();
 }
 
 }