[giow] (1) Make a.ping and area.ping use DOMSettableTokenList based on #whatwg feedback. Hopefully no content relies on their existing implementations; if they do let me know and we'll back this out.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=24183
Affected topics: DOM APIs

git-svn-id: http://svn.whatwg.org/webapps@8369 340c8d12-0b0e-0410-8428-c7bf67bfef74