DocumentTimeline doesn't need to unregister itself from DocumentTimelinesController on destruction since the DocumentTimelinesController is using a WeakHashSet.
Pull request: https://github.com/WebKit/WebKit/pull/11833
Committed 262002@main (13c816f5c7b2): <https://commits.webkit.org/262002@main> Reviewed commits have been landed. Closing PR #11833 and removing active labels.
<rdar://problem/107116012>