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

Source/core/layout/line/LineBoxList.h

 /*
  * Copyright (C) 2009 Apple 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 20 matching lines @@
 #define LineBoxList_h
 
 #include "core/layout/LayoutObject.h"
 
 namespace blink {
 
 class InlineFlowBox;
 class LineBoxList {
 public:
     LineBoxList()
-        : m_firstLineBox(0)
-        , m_lastLineBox(0)
+        : m_firstLineBox(nullptr)
+        , m_lastLineBox(nullptr)
     {
     }
 
 #if ENABLE(ASSERT)
     ~LineBoxList();
 #endif
 
     InlineFlowBox* firstLineBox() const { return m_firstLineBox; }
     InlineFlowBox* lastLineBox() const { return m_lastLineBox; }
 
@@ skipping 28 matching lines @@
 
 #if !ENABLE(ASSERT)
 inline void LineBoxList::checkConsistency() const
 {
 }
 #endif
 
 } // namespace blink
 
 #endif // LineBoxList_h