GitLab

AverageLag are calculated from latency_info.scroll_update_delta.
It was set from GestureScrollUpdate event's delta_y; however, scroll
prediction is done after scroll_update_delta set, which means the
AverageLag did not count in the prediction result.

This CL adds setting the scroll_update_delta from GSU, so it will
count in the prediction change as well.

Bug: 836352
Change-Id: I979e0da617dbfdfa6735aee33958cb9dac9b8331
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1509102Reviewed-by: Navid Zolghadr <nzolghadr@chromium.org>
Commit-Queue: Ella Ge <eirage@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638732}