Use C++11 features in core/html

Source/core/html/HTMLImageElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google 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 533 matching lines @@
     // If the usemap attribute starts with '#', it refers to a map element in the document.
     if (usemap[0] == '#')
         return false;
 
     return document().completeURL(stripLeadingAndTrailingHTMLSpaces(usemap)).isEmpty();
 }
 
 Image* HTMLImageElement::imageContents()
 {
     if (!imageLoader().imageComplete())
-        return 0;
+        return nullptr;
 
     return imageLoader().image()->image();
 }
 
 bool HTMLImageElement::isInteractiveContent() const
 {
     return fastHasAttribute(usemapAttr);
 }
 
 PassRefPtr<Image> HTMLImageElement::getSourceImageForCanvas(SourceImageMode, SourceImageStatus* status) const
@@ skipping 81 matching lines @@
     }
     imageLoader().updateFromElement(behavior);
 }
 
 const KURL& HTMLImageElement::sourceURL() const
 {
     return cachedImage()->response().url();
 }
 
 }