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

Source/core/layout/line/WordMeasurement.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) 2013 Adobe Systems Incorporated.
  *
  * 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 16 matching lines @@
 #include "platform/fonts/SimpleFontData.h"
 #include "wtf/HashSet.h"
 
 namespace blink {
 
 class LayoutText;
 
 class WordMeasurement {
 public:
     WordMeasurement()
-        : layoutText(0)
+        : layoutText(nullptr)
         , width(0)
         , startOffset(0)
         , endOffset(0)
     {
     }
 
     LayoutText* layoutText;
     float width;
     int startOffset;
     int endOffset;
     HashSet<const SimpleFontData*> fallbackFonts;
 };
 
 } // namespace blink
 
 #endif // WordMeasurement_h