<label> should support form association by parser

Source/core/html/FormAssociatedElement.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 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 38 matching lines @@
     void deref() { derefFormAssociatedElement(); }
 #endif
 
     static HTMLFormElement* findAssociatedForm(const HTMLElement*);
     HTMLFormElement* form() const { return m_form.get(); }
     ValidityState* validity();
 
     virtual bool isFormControlElement() const = 0;
     virtual bool isFormControlElementWithState() const;
     virtual bool isEnumeratable() const = 0;
+    virtual bool isLabelElement() const { return false; }
 
     // Returns the 'name' attribute value. If this element has no name
     // attribute, it returns an empty string instead of null string.
     // Note that the 'name' IDL attribute doesn't use this function.
     virtual const AtomicString& name() const;
 
     // Override in derived classes to get the encoded name=value pair for submitting.
     // Return true for a successful control (see HTML4-17.13.2).
     virtual bool appendFormData(FormDataList&, bool) { return false; }
 
@@ skipping 69 matching lines @@
 };
 
 HTMLElement* toHTMLElement(FormAssociatedElement*);
 HTMLElement& toHTMLElement(FormAssociatedElement&);
 const HTMLElement* toHTMLElement(const FormAssociatedElement*);
 const HTMLElement& toHTMLElement(const FormAssociatedElement&);
 
 } // namespace
 
 #endif // FormAssociatedElement_h