Use C++11 features in core/html

Source/core/html/HTMLMapElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 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
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 63 matching lines @@
         ASSERT(isHTMLImageElement(curr));
 
         // The HTMLImageElement's useMap() value includes the '#' symbol at the beginning,
         // which has to be stripped off.
         HTMLImageElement& imageElement = toHTMLImageElement(*curr);
         String useMapName = imageElement.getAttribute(usemapAttr).string().substring(1);
         if (equalIgnoringCase(useMapName, m_name))
             return &imageElement;
     }
 
-    return 0;
+    return nullptr;
 }
 
 void HTMLMapElement::parseAttribute(const QualifiedName& name, const AtomicString& value)
 {
     // FIXME: This logic seems wrong for XML documents.
     // Either the id or name will be used depending on the order the attributes are parsed.
 
     if (isIdAttributeName(name) || name == nameAttr) {
         if (isIdAttributeName(name)) {
             // Call base class so that hasID bit gets set.
@@ skipping 29 matching lines @@
 }
 
 void HTMLMapElement::removedFrom(ContainerNode* insertionPoint)
 {
     if (insertionPoint->inDocument())
         treeScope().removeImageMap(this);
     HTMLElement::removedFrom(insertionPoint);
 }
 
 }