Node: Use FINAL instead of the non-virtual shadowing hack.
<http://webkit.org/b/115995>

Reviewed by Anders Carlsson.

Decorate Element/Attr implementations of prefix/localName/namespaceURI getters with FINAL
so that call sites with a more specific pointer type than Node* can avoid the virtual dispatch.

* dom/Attr.h:
* dom/Element.h:
* dom/Node.cpp:
* dom/Node.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149974 268f45cc-cd09-0410-ab3c-d52691b4dbfc