Use C++11 features in core/html

Source/core/html/HTMLFrameSetElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Simon Hausmann (hausmann@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2006, 2009, 2010 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
@@ skipping 196 matching lines @@
     if (needsStyleRecalc() && renderer()) {
         renderer()->setNeedsLayoutAndFullPaintInvalidation();
         clearNeedsStyleRecalc();
     }
 }
 
 LocalDOMWindow* HTMLFrameSetElement::anonymousNamedGetter(const AtomicString& name)
 {
     Element* frameElement = children()->namedItem(name);
     if (!isHTMLFrameElement(frameElement))
-        return 0;
+        return nullptr;
     Document* document = toHTMLFrameElement(frameElement)->contentDocument();
     if (!document || !document->frame())
-        return 0;
+        return nullptr;
     return document->domWindow();
 }
 
 } // namespace blink