This patch begins to make changes that make going back and forward in a site isolated iframe work correctly.
<rdar://problem/128420789>
Pull request: https://github.com/WebKit/WebKit/pull/28806
Committed 279152@main (1085dea9ba41): <https://commits.webkit.org/279152@main> Reviewed commits have been landed. Closing PR #28806 and removing active labels.