ElementRareAnimationData and CSSTransition still use CSSPropertyID instead of AnimatableProperty, as well as Styleable which deals with data structures exposed through ElementRareAnimationData. We need to make those adopt AnimatableProperty in order to support CSS Transitions of custom properties (see bug 249399).
Pull request: https://github.com/WebKit/WebKit/pull/7856
Committed 258120@main (79a040808a38): <https://commits.webkit.org/258120@main> Reviewed commits have been landed. Closing PR #7856 and removing active labels.
<rdar://problem/103542359>