[giow] (3) Make clear that .crossOrigin doesn't return '' for the Anonymous state.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=19574
Affected topics: HTML

git-svn-id: http://svn.whatwg.org/webapps@7951 340c8d12-0b0e-0410-8428-c7bf67bfef74