The work to run accelerated animations on a thread (see bug 250970) needs a preference to control whether that feature is enabled.
<rdar://problem/104526819>
Pull request: https://github.com/WebKit/WebKit/pull/8951
Committed 259378@main (8c0586df0275): <https://commits.webkit.org/259378@main> Reviewed commits have been landed. Closing PR #8951 and removing active labels.