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

Source/core/layout/LayoutImage.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2006 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * 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 56 matching lines @@
             imageChanged(m_imageResource->imagePtr());
     }
 
     virtual const char* name() const override { return "LayoutImage"; }
 
 protected:
     virtual bool needsPreferredWidthsRecalculation() const override final;
     virtual LayoutBox* embeddedContentBox() const override final;
     virtual void computeIntrinsicRatioInformation(FloatSize& intrinsicSize, double& intrinsicRatio) const override final;
 
-    virtual void imageChanged(WrappedImagePtr, const IntRect* = 0) override;
+    virtual void imageChanged(WrappedImagePtr, const IntRect* = nullptr) override;
 
     virtual void paint(const PaintInfo&, const LayoutPoint&) override final;
 
     virtual void layout() override;
     virtual bool updateImageLoadingPriorities() override final;
 
     virtual bool isOfType(LayoutObjectType type) const override { return type == LayoutObjectLayoutImage || LayoutReplaced::isOfType(type); }
 
     virtual void willBeDestroyed() override;
 
@@ skipping 24 matching lines @@
     bool m_didIncrementVisuallyNonEmptyPixelCount;
     bool m_isGeneratedContent;
     float m_imageDevicePixelRatio;
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutImage, isLayoutImage());
 
 } // namespace blink
 
 #endif // LayoutImage_h