Currently WorkletAnimations can only be run from the compositor thread, which requires their targets, as well as the target of any ScrollTimeline they use, to be composited.
It will be necessary for a full release to have fallback behavior such that WorkletAnimations can be controlled/run on the main thread, e.g. for properties that cannot be animated compositor-side.
Comment 1 by majidvp@chromium.org
, May 24 2018