GitLab

I didn't find out the exact cause, but something about the ARC app was
updating the backdrop many times during the course of a swipe, and was
probably creating a new one which did not have an transform or opacity
changes. This happens for regular windows as well, so instead, pause
updates during a home launcher drag.

Test: manual
Bug: 1018125
Change-Id: I1d933921f8c17410fb6a8c81f96c94e93fc59955
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1884578Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#711035}