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

Source/core/layout/CounterNode.h

 /*
  * Copyright (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 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,
@@ skipping 44 matching lines @@
     // Invalidates the text in the layoutObjects of this counter, if any.
     void resetLayoutObjects();
 
     CounterNode* parent() const { return m_parent; }
     CounterNode* previousSibling() const { return m_previousSibling; }
     CounterNode* nextSibling() const { return m_nextSibling; }
     CounterNode* firstChild() const { return m_firstChild; }
     CounterNode* lastChild() const { return m_lastChild; }
     CounterNode* lastDescendant() const;
     CounterNode* previousInPreOrder() const;
-    CounterNode* nextInPreOrder(const CounterNode* stayWithin = 0) const;
-    CounterNode* nextInPreOrderAfterChildren(const CounterNode* stayWithin = 0) const;
+    CounterNode* nextInPreOrder(const CounterNode* stayWithin = nullptr) const;
+    CounterNode* nextInPreOrderAfterChildren(const CounterNode* stayWithin = nullptr) const;
 
     void insertAfter(CounterNode* newChild, CounterNode* beforeChild, const AtomicString& identifier);
 
     // identifier must match the identifier of this counter.
     void removeChild(CounterNode*);
 
 private:
     CounterNode(LayoutObject&, bool isReset, int value);
     int computeCountInParent() const;
     // Invalidates the text in the layoutObject of this counter, if any,
@@ skipping 15 matching lines @@
 };
 
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showCounterTree(const blink::CounterNode*);
 #endif
 
 #endif // CounterNode_h