With UI-side compositing enabled, fast/scrolling/mac/momentum-animator-end-event-stops.html reveals a bug where only the first wheel event is dispatched to JS because `WebPage::wheelEvent()` never calls the `send(Messages::WebPageProxy::DidReceiveEvent()` so subsequent events are held up via WebWheelEventCoalescer::shouldDispatchEvent() having a non-empty m_eventsBeingProcessed.
<rdar://problem/104061538>
Fixed via bug 250752. *** This bug has been marked as a duplicate of bug 250752 ***