overview: Do not animate windows hidden behind a backdrop.

Windows which have a backdrop should be treated as if their bounds was
size of work area, otherwise windows behind them which may be maximized
may be animated, even though they are hidden.

Test: manual
Bug: 828997
Change-Id: Ie828da6e169ca1e79eacd0a28931a144ab8dbed6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1614714
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662379}
4 files changed