[giow] (0) Make non-modal dialogs not center automatically.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=20418
Affected topics: CSS, DOM APIs, HTML

git-svn-id: http://svn.whatwg.org/webapps@8457 340c8d12-0b0e-0410-8428-c7bf67bfef74