Today API::HTTPCookieStore::deleteAllCookies just dispatches its completion handler on the main loop while the cookies may not have been deleted yet.
Pull request: https://github.com/WebKit/WebKit/pull/865
<rdar://problem/94057004>
Closing as it was fixed in https://github.com/WebKit/WebKit/commit/b7202854b8f9f74f2295bd478e632695b7470524