C++11: Replace 0 with nullptr where applicable in layout code.

Source/core/layout/svg/LayoutSVGImage.h

 /*
  * Copyright (C) 2006 Alexander Kellett <lypanov@kde.org>
  * Copyright (C) 2006, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Rob Buis <buis@kde.org>
  * Copyright (C) 2009 Google, Inc.
  * Copyright (C) 2010 Patrick Gansterer <paroga@paroga.com>
  *
  * 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
@@ skipping 42 matching lines @@
     virtual const char* name() const override { return "LayoutSVGImage"; }
 
 protected:
     virtual void willBeDestroyed() override;
 
 private:
     virtual FloatRect strokeBoundingBox() const override { return m_objectBoundingBox; }
 
     virtual void addFocusRingRects(Vector<LayoutRect>&, const LayoutPoint& additionalOffset) const override;
 
-    virtual void imageChanged(WrappedImagePtr, const IntRect* = 0) override;
+    virtual void imageChanged(WrappedImagePtr, const IntRect* = nullptr) override;
 
     virtual void layout() override;
     virtual void paint(const PaintInfo&, const LayoutPoint&) override;
 
     FloatSize computeImageViewportSize(ImageResource&) const;
 
     virtual bool nodeAtFloatPoint(HitTestResult&, const FloatPoint& pointInParent, HitTestAction) override;
 
     virtual AffineTransform localTransform() const override { return m_localTransform; }
 
     bool m_needsBoundariesUpdate : 1;
     bool m_needsTransformUpdate : 1;
     AffineTransform m_localTransform;
     FloatRect m_objectBoundingBox;
     OwnPtr<LayoutImageResource> m_imageResource;
 
     RefPtr<const SkPicture> m_bufferedForeground;
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutSVGImage, isSVGImage());
 
 } // namespace blink
 
 #endif // LayoutSVGImage_h