We need a dedicated flag for the KeyframeEffect.iterationComposite property as that property did not make it to Web Animations 1.0 and should not be enabled together with KeyframeEffect.composite.
Pull request: https://github.com/WebKit/WebKit/pull/848
Committed r294579 (250816@main): <https://commits.webkit.org/250816@main> Reviewed commits have been landed. Closing PR #848 and removing active labels.
<rdar://problem/93678419>
This caused bug 242178.