[e] (0) Reframe the 'update the rendering' step so we can add substeps.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=26636
Affected topics: DOM APIs

git-svn-id: https://svn.whatwg.org/webapps@8782 340c8d12-0b0e-0410-8428-c7bf67bfef74