GitLab

This CL adds two metrics for scroll event prediction to help analyse
prediction behavior, Scroll.OverPredict and Scroll.UnderPredict.

The new metrics only records the y direction difference of prediction
result instead of euclidean distance, since y direction scroll is more
popular and only record one direction is easier for determine over/under
predict.


Bug: 836352
Change-Id: I2f83fa5404b02c52f8856dfb64fa0151b7b686d6
Reviewed-on: https://chromium-review.googlesource.com/c/1354314Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Reviewed-by: Navid Zolghadr <nzolghadr@chromium.org>
Commit-Queue: Ella Ge <eirage@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612401}