We need to integrate DOM timers with HTML5 event loop.
<rdar://problem/56396746>
Created attachment 381366 [details] WIP
Hm... integrating SuspendableTimerBase with EventLoop is a bit tricky because at the time of Document creation, we don't know to which EventLoop we belong due to the security origin of the document not being initialized until later in the constructor yet DocumentEventQueue relies on SuspendableTimerBase. We may need to do more refactoring to make this work.