Use C++11 features in core/html

Source/core/html/HTMLAreaElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2009, 2011 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 158 matching lines @@
             break;
     }
 
     return path;
 }
 
 HTMLImageElement* HTMLAreaElement::imageElement() const
 {
     if (HTMLMapElement* mapElement = Traversal<HTMLMapElement>::firstAncestor(*this))
         return mapElement->imageElement();
-    return 0;
+    return nullptr;
 }
 
 bool HTMLAreaElement::isKeyboardFocusable() const
 {
     return isFocusable();
 }
 
 bool HTMLAreaElement::isMouseFocusable() const
 {
     return isFocusable();
@@ skipping 32 matching lines @@
         return;
 
     HTMLImageElement* imageElement = this->imageElement();
     if (!imageElement)
         return;
 
     imageElement->updateFocusAppearance(restorePreviousSelection);
 }
 
 }