[giow] (1) Allow browsers to act like video stalled during navigation, rather than aborted.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=18788
Affected topics: Video and Audio

git-svn-id: http://svn.whatwg.org/webapps@7721 340c8d12-0b0e-0410-8428-c7bf67bfef74