CSSAnimationEvent and CSSTransitionEvent both have the same `m_elapsedTime` and `m_pseudoElement` members, they should inherit from a similar base class.
Pull request: https://github.com/WebKit/WebKit/pull/6834
Committed 257047@main (5b655cd9d573): <https://commits.webkit.org/257047@main> Reviewed commits have been landed. Closing PR #6834 and removing active labels.
<rdar://problem/102690285>