REGRESSION (UI-side compositing) changing between non-overlay and overlay scrollbars should adjust the size of the scrollable area
<rdar://problem/117507268>
Pull request: https://github.com/WebKit/WebKit/pull/19576
Committed 276439@main (81451dabde97): <https://commits.webkit.org/276439@main> Reviewed commits have been landed. Closing PR #19576 and removing active labels.