Unreviewed functionality fix for ports enabling the MicroData feature.

* html/DOMSettableTokenList.idl: Add the SkipVTableValidation IDL attribute to the DOMSettableTokenList interface.
This removes crashes in the MicroData layout tests that are occurring on EFL and GTK builders, the two ports being
the only ports that enable this feature.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@148269 268f45cc-cd09-0410-ab3c-d52691b4dbfc