Spec: https://html.spec.whatwg.org/multipage/#timer-task-source

Currently, we handle messages coming-in from the timer dispatcher(in the constellation) as a MixedMessage either by the script-thread at

or the worker at

Those message are initially coming over IPC and then routed onto a threaded channel, at

and and for ServiceWorker it seems timeouts aren't supported yet?

In all of these cases, we should instead route the incoming IPC message into a task queued using the newly implemented timer-task-source, that should be added to https://github.com/servo/servo/tree/master/components/script/task_source