Reading through the changelog of the ticket, it looks like they're still making their mind up about keeping the old function
window.autosave = function(){};
in the code for backwards compatibility. So many plugins currently use it that it would break so many websites with the update.
A patch was put in place but has not been added to the master [#25272.6.patch][1]
Best idea would be to ask within the ticket and hope that the backwards compatibility is kept in place until there is a surefire way documented.