GitLab

This was because the label was previous parented to AlwaysOnTop
container. This was fine before when there was no scrolling, but now
with scrolling, the label should be parented to the same container
as the regular windows, so that it snapped window can be stacked
ontop of it as well.

Test: added test, manual
Bug: 1017882
Change-Id: I8b3d2d50f814e1b1c631372478d6ddd16bcc5608
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1880177Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709517}