Fix sampling of keyframe effect's in the before phase
Pass the limit direction to apply at discontinuous boundaries of the
timing function to the sampling methods to follow the special
handling of the before phase on step timing functions defined in
https://drafts.csswg.org/css-easing/#step-easing-algo
Bug: 40870829
Change-Id: I56128d70670dc0e145b5e19a29b1a898b3f0105e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5630828
Reviewed-by: Robert Flack flackr@chromium.org
Commit-Queue: Kevin Ellis kevers@chromium.org
Cr-Commit-Position: refs/heads/main@{#1317089}