Replace elementHasLegalLinkAttribute() helper with virtual function

Source/core/html/forms/ImageInputType.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) 2012 Samsung Electronics. 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 217 matching lines @@
                 return imageLoader->image()->imageSizeForRenderer(element->renderer(), 1).width();
         }
     }
 
     element->document().updateLayout();
 
     RenderBox* box = element->renderBox();
     return box ? adjustForAbsoluteZoom(box->contentWidth(), box) : 0;
 }
 
+bool ImageInputType::hasLegalLinkAttribute(const QualifiedName& name) const
+{
+    return name == srcAttr || BaseButtonInputType::hasLegalLinkAttribute(name);
+}
+
 } // namespace WebCore