Use C++11 features in core/html

Source/core/html/HTMLStyleElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2010 Apple Inc. All rights reserved.
  *           (C) 2007 Rob Buis (buis@kde.org)
  *
  * 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 115 matching lines @@
 }
 
 const AtomicString& HTMLStyleElement::type() const
 {
     return getAttribute(typeAttr);
 }
 
 ContainerNode* HTMLStyleElement::scopingNode()
 {
     if (!inDocument())
-        return 0;
+        return nullptr;
 
     if (isInShadowTree())
         return containingShadowRoot();
 
     return &document();
 }
 
 void HTMLStyleElement::dispatchPendingLoadEvents()
 {
     styleLoadEventSender().dispatchPendingEvents();
@@ skipping 28 matching lines @@
         styleSheet->setDisabled(setDisabled);
 }
 
 void HTMLStyleElement::trace(Visitor* visitor)
 {
     StyleElement::trace(visitor);
     HTMLElement::trace(visitor);
 }
 
 }