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

Source/core/layout/LayoutRubyBase.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 @@
     virtual bool isOfType(LayoutObjectType type) const override { return type == LayoutObjectRubyBase || LayoutBlockFlow::isOfType(type); }
 
     virtual bool isChildAllowed(LayoutObject*, const ComputedStyle&) const override;
 
 private:
     LayoutRubyBase();
 
     virtual ETextAlign textAlignmentForLine(bool endsWithSoftBreak) const override;
     virtual void adjustInlineDirectionLineBounds(unsigned expansionOpportunityCount, LayoutUnit& logicalLeft, LayoutUnit& logicalWidth) const override;
 
-    void moveChildren(LayoutRubyBase* toBase, LayoutObject* beforeChild = 0);
-    void moveInlineChildren(LayoutRubyBase* toBase, LayoutObject* beforeChild = 0);
-    void moveBlockChildren(LayoutRubyBase* toBase, LayoutObject* beforeChild = 0);
+    void moveChildren(LayoutRubyBase* toBase, LayoutObject* beforeChild = nullptr);
+    void moveInlineChildren(LayoutRubyBase* toBase, LayoutObject* beforeChild = nullptr);
+    void moveBlockChildren(LayoutRubyBase* toBase, LayoutObject* beforeChild = nullptr);
 
     // Allow LayoutRubyRun to manipulate the children within ruby bases.
     friend class LayoutRubyRun;
 };
 
 } // namespace blink
 
 #endif // LayoutRubyBase_h