There doesn't seem to be any hits on Github aside from WebKit checkouts: https://github.com/search?q=%3A-webkit-full-screen-controls-hidden&type=code
<rdar://problem/121323330>
Pull request: https://github.com/WebKit/WebKit/pull/23362
Committed 273619@main (b706dea06d35): <https://commits.webkit.org/273619@main> Reviewed commits have been landed. Closing PR #23362 and removing active labels.