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

Source/core/layout/LayoutRubyRun.h

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 37 matching lines @@
     bool hasRubyText() const;
     bool hasRubyBase() const;
     LayoutRubyText* rubyText() const;
     LayoutRubyBase* rubyBase() const;
     LayoutRubyBase* rubyBaseSafe(); // creates the base if it doesn't already exist
 
     virtual LayoutObject* layoutSpecialExcludedChild(bool relayoutChildren, SubtreeLayoutScope&) override;
     virtual void layout() override;
 
     virtual bool isChildAllowed(LayoutObject*, const ComputedStyle&) const override;
-    virtual void addChild(LayoutObject* child, LayoutObject* beforeChild = 0) override;
+    virtual void addChild(LayoutObject* child, LayoutObject* beforeChild = nullptr) override;
     virtual void removeChild(LayoutObject* child) override;
 
     void getOverhang(bool firstLine, LayoutObject* startLayoutObject, LayoutObject* endLayoutObject, int& startOverhang, int& endOverhang) const;
 
     static LayoutRubyRun* staticCreateRubyRun(const LayoutObject* parentRuby);
 
     virtual const char* name() const override { return "LayoutRubyRun"; }
 
 protected:
     LayoutRubyBase* createRubyBase() const;
 
 private:
     LayoutRubyRun();
 
     virtual bool isOfType(LayoutObjectType type) const override { return type == LayoutObjectRubyRun || LayoutBlockFlow::isOfType(type); }
     virtual bool createsAnonymousWrapper() const override { return true; }
     virtual void removeLeftoverAnonymousBlock(LayoutBlock*) override { }
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutRubyRun, isRubyRun());
 
 } // namespace blink
 
 #endif // LayoutRubyRun_h