desks: Fix issues with backdrop showing up in multiprofile.

There are two issues, one is the backdrop showing up when an ARC app
is maximized on another desk on another profile. See comment 9 in the
bug for more details.

The other issue is when the a desk is selected in overview, which on
the non-active profile contains a maximized ARC app. The backdrop will
appear (outside of overview).

Fixed: 1184014
Test: manual
Change-Id: I993d36193bf9afd2a103f609ea53851fe1a3d9ee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2771302


Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#864690}