Their role was to prevent visible shifts while entering fullscreen, but this may not be needed with the newest fullscreen CSS.
<rdar://problem/100793009>
Pull request: https://github.com/WebKit/WebKit/pull/5014
Pull request: https://github.com/WebKit/WebKit/pull/5434
Committed 255641@main (5ca2229ca678): <https://commits.webkit.org/255641@main> Reviewed commits have been landed. Closing PR #5434 and removing active labels.