Having NSScrollerImp objects in the web process doesn't make sense (since they need CALayers to render). We need to refactor ScrollbarsController in a way that makes sense with UI-side compositing.
This is testable via gestures like "two fingers down on the trackpad" which should flash the scrollers.
<rdar://problem/104836240>
Fixed via https://bugs.webkit.org/show_bug.cgi?id=253684 *** This bug has been marked as a duplicate of bug 253684 ***