Using SetDelay on an existing ONE_SHOT timer is a convenient way to re-schedule a timer that did not yet fire.
However, if the timer fired already but the callback did not yet fully execute and the caller still thinks
to have a pending timer, our internal book-keeping will already have removed the timer from the list and
SetDelay will not re-activate the timer for us.
namedTimer instead seems to expect to always have activated a timer when called. We can still reuse the existing
timer object but need to always call initWithCallback which takes care of all the book-keeping details for us.
Note that this does not change much in terms of effort, as also SetDelay removes and then re-adds the timer from
and to the active timers list.
Differential Revision: https://phabricator.services.mozilla.com/D247440
ddeb6c7c01