Currently the code to determine the interpolation interval, the "from" and "to" keyframes, is contained within `KeyframeEffect::setAnimatedPropertiesInStyle()`. As part of the work on threaded animation resolution (see bug 250970), we will need to share this logic with `AcceleratedEffect` as well. Now that we have a shared concept of a keyframe (see bug 264747), we can add a method to `KeyframeInterpolation` for that purpose with whatever virtual methods are required on a new share base class for `AcceleratedEffect` and `KeyframeEffect`.
Pull request: https://github.com/WebKit/WebKit/pull/20428
Committed 270692@main (9bafc5fbd3e0): <https://commits.webkit.org/270692@main> Reviewed commits have been landed. Closing PR #20428 and removing active labels.
<rdar://problem/118375013>