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

Source/core/layout/line/TrailingObjects.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All right reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) 2014 Adobe Systems Inc.
  *
  * 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.
@@ skipping 37 matching lines @@
 // In both of the above snippets the inline and the positioned object occur after a trailing space
 // and before a space that will cause our line breaking algorithm to start ignoring spaces. When it
 // does that we want to ensure that the inline/positioned object gets a linebox and that it is part
 // of the collapsed whitespace. So to achieve this we use appendObjectIfNeeded() to keep track of
 // objects encountered after a trailing whitespace and updateMidpointsForTrailingObjects() to put
 // them in the right place when we start ignoring surplus whitespace.
 
 class TrailingObjects {
 public:
     TrailingObjects()
-        : m_whitespace(0)
+        : m_whitespace(nullptr)
     {
     }
 
     void setTrailingWhitespace(LayoutText* whitespace)
     {
         ASSERT(whitespace);
         m_whitespace = whitespace;
     }
 
     void clear()
     {
-        m_whitespace = 0;
+        m_whitespace = nullptr;
         // Using resize(0) rather than clear() here saves 2% on
         // PerformanceTests/Layout/line-layout.html because we avoid freeing and
         // re-allocating the underlying buffer repeatedly.
         m_objects.resize(0);
     }
 
     void appendObjectIfNeeded(LayoutObject* object)
     {
         if (m_whitespace)
             m_objects.append(object);
     }
 
     enum CollapseFirstSpaceOrNot { DoNotCollapseFirstSpace, CollapseFirstSpace };
 
     void updateMidpointsForTrailingObjects(LineMidpointState&, const InlineIterator& lBreak, CollapseFirstSpaceOrNot);
 
 private:
     LayoutText* m_whitespace;
     Vector<LayoutObject*, 4> m_objects;
 };
 
 }
 
 #endif // TrailingObjects_h