GitLab

Update ScrollTimeline to use post-snapped scroll offsets instead of pre-snapped
one. This fixes jitter when scroll-linked worklet animation is trying to
position items against the scroll offset.

Background:
Scrolling layers are pixel snapped which means they are shifted so that
they get aligned to pixel boundaries. This means that the raw scroll offset
of a scrolling layer is not exactly what is display on the screen.

The snapping is done by adjusting the effective transform of the associated
TransformNode for this scrolling element.

Previously ScrollTimeline would use raw scroll offset to compute its time.
This patch introduces a new method on the ScrollTree that will use the info
from TransformNode to calculate an effective scroll offset that represents the
post-snapped position of the scrolling node.

Bug: 585458
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I30bb052d8cfef8a32ec1a613921d7594bef3c982
Reviewed-on: https://chromium-review.googlesource.com/1153583
Commit-Queue: Majid Valipour <majidvp@chromium.org>
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Reviewed-by: Ali Juma <ajuma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583819}