The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/cdba22e6b710cb2d8e1b8c97f2decaa3d208cc86

commit cdba22e6b710cb2d8e1b8c97f2decaa3d208cc86
Author: Yuichiro Hanada <yhanada@chromium.org>
Date: Fri Jan 19 00:27:13 2018

exo: Discard a reserved keyboard shortcut only if it's enabled.

When seeing a reserved keyboard shortcut, exo display server sends
keyboard leave/enter event with pressed keys information instead of
key events.

      only one IME is enabled.

Bug: 801088
Test: Manual. Confirm that Ctrl-Space is sent to Android apps when
Change-Id: I207434b45690f231601cb6187e35a806f8c69f89
Reviewed-on: https://chromium-review.googlesource.com/866655
Reviewed-by: David Reveman <reveman@chromium.org>
Commit-Queue: Yuichiro Hanada <yhanada@chromium.org>
Cr-Commit-Position: refs/heads/master@{#530360}
[modify] https://crrev.com/cdba22e6b710cb2d8e1b8c97f2decaa3d208cc86/components/exo/keyboard.cc

As we moved the filtering code into the container side, the issue came back.
I haven't came up with how to fix the issue in the container side because the container doesn't know whether a key event is an active shortcut or not.