[giow] (2) Try to reduce race conditions involving media elements and the 'load' event.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=24353
Affected topics: Video and Audio

git-svn-id: http://svn.whatwg.org/webapps@8434 340c8d12-0b0e-0410-8428-c7bf67bfef74