[giow] (1) Integrate with new promise stuff better
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=25662
Affected topics: Canvas, Security

git-svn-id: https://svn.whatwg.org/webapps@8804 340c8d12-0b0e-0410-8428-c7bf67bfef74