[giow] (1) Match reality
Affected topics: Canvas

git-svn-id: http://svn.whatwg.org/webapps@7865 340c8d12-0b0e-0410-8428-c7bf67bfef74
[giow] (1) Mark certain elements as hidden for ARIA purposes too.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=21428
Affected topics: HTML

git-svn-id: http://svn.whatwg.org/webapps@7866 340c8d12-0b0e-0410-8428-c7bf67bfef74