Pass PageIdentifier to the page via PageConfiguration object so the Page has an associated identifier at WebCore level. Previously, we'd have to go via the FrameLoaderClient to retrieve the pageID. As part of this change, pages now have an identifiers even when using WebKitLegacy.
Pull request: https://github.com/WebKit/WebKit/pull/13296
Committed 263596@main (6411b42f170e): <https://commits.webkit.org/263596@main> Reviewed commits have been landed. Closing PR #13296 and removing active labels.
<rdar://problem/108797157>