Toggling Timeline "Stop when page loads" to on should stop (immediately or soon) any active recording if already past the load event I'd suggest if after load tickling the dead timeout so we would stop within 2s.
Created attachment 363435 [details] Patch
Created attachment 363486 [details] Patch
Comment on attachment 363486 [details] Patch r=me, Nice!
Comment on attachment 363486 [details] Patch Clearing flags on attachment: 363486 Committed r242370: <https://trac.webkit.org/changeset/242370>
All reviewed patches have been landed. Closing bug.
<rdar://problem/48572456>