Avoid HashSet copy in DocumentTimeline::applyPendingAcceleratedAnimations().
Pull request: https://github.com/WebKit/WebKit/pull/11844
Committed 262007@main (821a561a950a): <https://commits.webkit.org/262007@main> Reviewed commits have been landed. Closing PR #11844 and removing active labels.
<rdar://problem/107117533>