Following #37946, script can use timer callbacks that are not Send, which means we can restructure the below:

I think we can mark the struct with crown::unrooted_must_root_lint::must_root, and have it own a Dom<GlobalScope>.

The task source could then be obtained from the global, but I think we should try to take this a bit further and try to avoid queueing a task, because when the timer is dispatched, we are already on the script-thread, so we can pretend to already be inside a queued task. This requires some looking into(things like entering a realm if necessary).