This method is not needed since KeyframeList::insert() already adds the properties of the newly inserted keyframe to KeyframeList::m_properties.
Pull request: https://github.com/WebKit/WebKit/pull/1649
Committed r295723 (251728@main): <https://commits.webkit.org/251728@main> Reviewed commits have been landed. Closing PR #1649 and removing active labels.
<rdar://problem/95665779>