@zachr could you block linux apps from consuming Alt+[ and Alt+]? I believe there's a sommelier config that supports that.

Just add them to the list of accelerators here:
https://chromium.googlesource.com/chromiumos/containers/cros-container-guest-tools/+/master/cros-sommelier-config/cros-sommelier-override.conf
and here:
https://chromium.googlesource.com/chromiumos/containers/cros-container-guest-tools/+/master/cros-sommelier-config/cros-sommelier-x-override.conf

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/containers/cros-container-guest-tools/+/21fd681e0aa4eb0626473a5bfc1ed2c9e906158d

commit 21fd681e0aa4eb0626473a5bfc1ed2c9e906158d
Author: Zach Reizner <zachr@google.com>
Date: Tue Sep 18 21:03:47 2018

cros-sommelier-config: Add accelerators for window snapping

The Alt+[ or Alt+] snap a window in Chrome OS. This change adds those
accelerators to the sommelier config so that they function for crostini
applications.

BUG= 881994 
TEST=Press Alt+[ or Alt+] while using crostini GUI apps.

Change-Id: I9ab20b213c317c95d28c11c655d46a7705dfe5dc
Reviewed-on: https://chromium-review.googlesource.com/1222388
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Zach Reizner <zachr@chromium.org>
Reviewed-by: David Reveman <reveman@chromium.org>
Reviewed-by: Stephen Barber <smbarber@chromium.org>

[modify] https://crrev.com/21fd681e0aa4eb0626473a5bfc1ed2c9e906158d/cros-sommelier-config/cros-sommelier-x-override.conf
[modify] https://crrev.com/21fd681e0aa4eb0626473a5bfc1ed2c9e906158d/cros-sommelier-config/cros-sommelier-override.conf