Apply FINAL to the Node hierarchy.
<http://webkit.org/b/115984>

Mostly from Blink r149454 by <cevans@chromium.org>
<http://src.chromium.org/viewvc/blink?view=revision&revision=149454>

A couple of the stable DOM/ microbenchmarks are perf positive on Linux clang:

    - CloneNodes time reduced from 162.4 to 156.5 ms.
    - CreateNodes time reduced from 113.9 to 104.9 ms.

* dom/: Beat things with the FINAL stick.
* html/: Ditto.
* svg/: Ditto.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149960 268f45cc-cd09-0410-ab3c-d52691b4dbfc