As described on the e-mail thread and document here:
https://groups.google.com/a/chromium.org/forum/#!topic/animations-dev/Uwx-y6rOJXs

Once we call animations asynchronously from issue 791280 we will allow animations to miss the current frame. We should record the time it takes animations to run as part of CompositorTimingHistory[1] and update Scheduler::BeginImplFrameWithDeadline[2] to attempt to allow time for animations to run (e.g. set commit deadline to be early enough to have time for Nth percentile of worklet runs with some upper bound on how long that can be).

This can be started before issue 791280 is resolved by getting the mutate times recorded, but the scheduler changes would need to wait until after.

[1] https://cs.chromium.org/chromium/src/cc/scheduler/compositor_timing_history.h?gsn=compositor_timing_history_&l=26
[2] https://cs.chromium.org/chromium/src/cc/scheduler/scheduler.cc?type=cs&sq=package:chromium&l=334