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

Source/core/layout/LayoutTableCell.h

 /*
  * Copyright (C) 1997 Martin Jones (mjones@kde.org)
  *           (C) 1997 Torben Weis (weis@kde.org)
  *           (C) 1998 Waldo Bastian (bastian@kde.org)
  *           (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2009, 2013 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
@@ skipping 226 matching lines @@
 
     virtual void willBeRemovedFromTree() override;
 
     virtual void updateLogicalWidth() override;
 
     virtual void paintBoxDecorationBackground(const PaintInfo&, const LayoutPoint&) override;
     virtual void paintMask(const PaintInfo&, const LayoutPoint&) override;
 
     virtual bool boxShadowShouldBeAppliedToBackground(BackgroundBleedAvoidance, InlineFlowBox*) const override;
 
-    virtual LayoutSize offsetFromContainer(const LayoutObject*, const LayoutPoint&, bool* offsetDependsOnPoint = 0) const override;
-    virtual LayoutRect clippedOverflowRectForPaintInvalidation(const LayoutBoxModelObject* paintInvalidationContainer, const PaintInvalidationState* = 0) const override;
+    virtual LayoutSize offsetFromContainer(const LayoutObject*, const LayoutPoint&, bool* offsetDependsOnPoint = nullptr) const override;
+    virtual LayoutRect clippedOverflowRectForPaintInvalidation(const LayoutBoxModelObject* paintInvalidationContainer, const PaintInvalidationState* = nullptr) const override;
     virtual void mapRectToPaintInvalidationBacking(const LayoutBoxModelObject* paintInvalidationContainer, LayoutRect&, const PaintInvalidationState*) const override;
 
     int borderHalfLeft(bool outer) const;
     int borderHalfRight(bool outer) const;
     int borderHalfTop(bool outer) const;
     int borderHalfBottom(bool outer) const;
 
     int borderHalfStart(bool outer) const;
     int borderHalfEnd(bool outer) const;
     int borderHalfBefore(bool outer) const;
@@ skipping 50 matching lines @@
 
 inline LayoutTableCell* LayoutTableRow::lastCell() const
 {
     ASSERT(children() == virtualChildren());
     return toLayoutTableCell(children()->lastChild());
 }
 
 } // namespace blink
 
 #endif // LayoutTableCell_h