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Previously this used to crash on a DCHECK. Now we should explicitly
disallow this, since an active window (requested to be moved to
another desk via shortcut for example) might be an always-on-top
window, or a pip.

BUG=988886
TEST=Added new test

Change-Id: Iacb3562e8cb8bd789b9e3a88ac6b977242a79c7e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1725549
Commit-Queue: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682337}