[giow] (1) Make <dialog> autofocus the first focusable control if there isn't one with autofocus=''.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=23366
Affected topics: CSS, DOM APIs

git-svn-id: http://svn.whatwg.org/webapps@8338 340c8d12-0b0e-0410-8428-c7bf67bfef74