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

Source/core/layout/LayoutTextCombine.h

 /*
  * Copyright (C) 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
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 27 matching lines @@
     float combinedTextWidth(const Font& font) const { return font.fontDescription().computedSize(); }
     const Font& originalFont() const { return parent()->style()->font(); }
     void transformToInlineCoordinates(GraphicsContext&, const LayoutRect& boxRect) const;
     void transformLayoutRect(LayoutRect& boxRect) const;
     LayoutUnit inlineWidthForLayout() const;
 
     virtual const char* name() const override { return "LayoutTextCombine"; }
 
 private:
     virtual bool isCombineText() const override { return true; }
-    virtual float width(unsigned from, unsigned length, const Font&, LayoutUnit xPosition, TextDirection, HashSet<const SimpleFontData*>* fallbackFonts = 0, GlyphOverflow* = 0) const override;
+    virtual float width(unsigned from, unsigned length, const Font&, LayoutUnit xPosition, TextDirection, HashSet<const SimpleFontData*>* fallbackFonts = nullptr, GlyphOverflow* = nullptr) const override;
     virtual void styleDidChange(StyleDifference, const ComputedStyle* oldStyle) override;
     virtual void setTextInternal(PassRefPtr<StringImpl>) override;
     void updateIsCombined();
 
     float offsetX(const LayoutRect& boxRect) const;
     float offsetXNoScale(const LayoutRect& boxRect) const;
 
     float m_combinedTextWidth;
     float m_scaleX;
     bool m_isCombined : 1;
@@ skipping 17 matching lines @@
 inline float LayoutTextCombine::offsetXNoScale(const LayoutRect& boxRect) const
 {
     ASSERT(!m_needsFontUpdate);
     return (boxRect.height() - m_combinedTextWidth) / 2;
 }
 
 
 } // namespace blink
 
 #endif // LayoutTextCombine_h