If any code within the shutdown code tries to access the lock (to remove buffer references) then we can deadlock.
<rdar://problem/102730950>
Pull request: https://github.com/WebKit/WebKit/pull/6878
Committed 257092@main (1f4c8acb5b7c): <https://commits.webkit.org/257092@main> Reviewed commits have been landed. Closing PR #6878 and removing active labels.