d46884a91159468d1e896d95399a54b601daa186  Main frame user interaction checks should work with site isolation

Classified as not security-relevant.
Triage note: Makes mainFrameDocumentHasHadUserInteraction() read a new HasHadUserInteraction field broadcast via Page top-document DocumentSyncData (setTopDocumentHasHadUserInteraction) instead of dereferencing mainFrameDocument() directly, so the signal is correct across processes under site isolation. Site-isolation plumbing for a web-audio autoplay quirk gate; no memory-safety/serious-policy bug.
This commit was flagged by the signal scorer and reviewed by AI (not a human). It is listed only so the triage is auditable; there is no root-cause analysis because this is not a vulnerability fix.

Structural signals: smartptr_member_added (+4.87), area:Source/WebCore/dom (+2.0), surgical (+1.3)