Drop MainThreadTaskDispatcher and use callOnMainThread() instead. There is a no need for a global Timer or a Deque of tasks.
Created attachment 430699 [details] Patch
Committed r278544 (238542@main): <https://commits.webkit.org/238542@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 430699 [details].
<rdar://problem/78935484>
It looks like the changes in https://trac.webkit.org/changeset/278544/webkit broke media/media-continues-playing-after-replace-source.html tracking in https://bugs.webkit.org/show_bug.cgi?id=226899