<rdar://problem/107499791>

WheelEventTestMonitor logging reveals: 21:25:40.660 73440 TileController::tileSize newSize=width=800 height=600 21:25:40.660 73440 WheelEventTestMonitor::clearAllTestDeferrals: cleared all test state. 21:25:40.660 73440 WheelEventTestMonitor::checkShouldFireCallbacks - have not yet seen any deferral reasons 21:25:40.660 73440 WheelEventTestMonitor::checkShouldFireCallbacks - have not yet seen any deferral reasons 21:25:40.660 73440 WheelEventTestMonitor::checkShouldFireCallbacks - have not yet seen any deferral reasons 21:25:40.660 73440 EventHandler::handleWheelEvent PlatformWheelEvent 0x7ff7b4cd74a0 at (100,120) deltaX 0.00 deltaY -10.00 phase "began" momentum phase "none" velocity width=0 height=0 processing steps [synchronous scrolling, blocking DOM event dispatch] 21:25:40.660 73440 (=) WheelEventTestMonitor::receivedWheelEventWithPhases: phase=began momentumPhase=none 21:25:40.660 73440 (=) WheelEventTestMonitor::deferForReason: id=0x75b0c0ae0, reason=handling wheel event on main thread 21:25:40.661 73440 LocalFrameView::setWasScrolledByUser at 1 21:25:40.661 73440 EventHandler::handleWheelEventInScrollableArea() RenderLayer 0x792002c60 300x500 - eventHandling [dispatched to DOM] -> gesture state non-blocking 21:25:40.661 73440 RenderLayer 0x792002c60 300x500 requestScrollPositionUpdate (0,10) 21:25:40.661 73440 RenderLayerScrollableArea [0] scrollTo (0,10) from (0,0) (is user scroll 1) 21:25:40.661 73440 ScrollableArea (RenderLayer 0x792002c60 300x500) handleWheelEvent - handled 1 21:25:40.661 73440 Element node 0x792004990 DIV 0x792004990 class='content' dispatchWheelEvent: (cancelable 1) defaultPrevented 0 defaultHandled 1 21:25:40.661 73440 (=) WheelEventTestMonitor::removeDeferralForReason: id=0x75b0c0ae0, reason=handling wheel event on main thread 21:25:40.661 73440 WebPage::wheelEvent - processing steps [synchronous scrolling, blocking DOM event dispatch] handled 1 21:25:40.661 73440 WheelEventTestMonitor::setTestCallbackAndStartMonitoring - expect end/cancel 0, expect momentum end 0 21:25:40.661 73440 WheelEventTestMonitor::checkShouldFireCallbacks: scrolling is idle, FIRING TEST so we're ending too early, when we've only seen the first event.

EventSendingController's m_sentWheelPhaseEndOrCancel and m_sentWheelMomentumPhaseEnd fail to get set when using `sendEventStream`

Pull request: https://github.com/WebKit/WebKit/pull/12339

Committed 262598@main (b9a297652bdc): <https://commits.webkit.org/262598@main> Reviewed commits have been landed. Closing PR #12339 and removing active labels.