The CSSKeyframesRule IDL interface has a length member that we do not expose.
Pull request: https://github.com/WebKit/WebKit/pull/10203
Committed 260400@main (e6fb2489c688): <https://commits.webkit.org/260400@main> Reviewed commits have been landed. Closing PR #10203 and removing active labels.
<rdar://problem/105565920>