Implement 'tabstop' as an HTML attribute

Source/core/html/HTMLElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004-2008, 2013, 2014 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2011 Motorola Mobility. 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
@@ skipping 326 matching lines @@
 
         for (size_t i = 0; i < WTF_ARRAY_LENGTH(attrToEventNames); i++)
             attributeNameToEventNameMap.set(attrToEventNames[i].attr.localName(), attrToEventNames[i].event);
     }
 
     return attributeNameToEventNameMap.get(attrName.localName());
 }
 
 void HTMLElement::parseAttribute(const QualifiedName& name, const AtomicString& value)
 {
-    if (name == tabindexAttr)
+    if (name == tabindexAttr || name == tabstopAttr)
         return Element::parseAttribute(name, value);
 
     if (name == dirAttr) {
         dirAttributeChanged(value);
     } else {
         const AtomicString& eventName = eventNameForAttributeName(name);
         if (!eventName.isNull())
             setAttributeEventListener(eventName, createAttributeEventListener(this, name, value, eventParameterName()));
     }
 }
@@ skipping 655 matching lines @@
 #ifndef NDEBUG
 
 // For use in the debugger
 void dumpInnerHTML(blink::HTMLElement*);
 
 void dumpInnerHTML(blink::HTMLElement* element)
 {
     printf("%s\n", element->innerHTML().ascii().data());
 }
 #endif