The work to run accelerated animations on a thread (see bug 250970) needs a compile-time flag to guard whether that feature is compiled.
<rdar://problem/104651299>
Pull request: https://github.com/WebKit/WebKit/pull/9125
Committed 259377@main (e64eea7dde9d): <https://commits.webkit.org/259377@main> Reviewed commits have been landed. Closing PR #9125 and removing active labels.