This change does some refactoring required for PSON for windows opened via window.open.
<rdar://problem/108333335>
Pull request: https://github.com/WebKit/WebKit/pull/12989
Committed 263375@main (b6dd5136a4bb): <https://commits.webkit.org/263375@main> Reviewed commits have been landed. Closing PR #12989 and removing active labels.