This patch introduces a mTopLevelWindowContextId field to
cookieJarSettings. The field caches the top-level window context id. We
use this field to check whether the top-level window is navigated away.
If so, we fallback to use partitionKey as the top URI when getting the
fingerprinting override because the top-level URI could be different in
this case.
Differential Revision: https://phabricator.services.mozilla.com/D203889
