[e] (0) Move a setTimeout() requirement from prose to IDL.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=24967
Affected topics: HTML Syntax and Parsing

git-svn-id: http://svn.whatwg.org/webapps@8535 340c8d12-0b0e-0410-8428-c7bf67bfef74