desks: Keep app list open when switching desks.

App list was closing because activating a new window closes the app list.
This CL addresses that by only activating windows on desk switch, if the
current active window is in the mru list (is a app window). If the
current active window is not an app, such as the app list, then we switch
desks without activating the mru window on the new desk. This would also
work on other windows built similarly, but the only one I'm aware of is
the app list.

Test: manual, added test
Change-Id: I31314800a4fd5c774d23148875e851377ef89f20
Fixed: 1138982
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2485566


Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819920}