[giow] (2) <details ontoggle=''> for when you open or close a <dialog>.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=22942
Affected topics: DOM APIs, HTML

git-svn-id: http://svn.whatwg.org/webapps@8251 340c8d12-0b0e-0410-8428-c7bf67bfef74