The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/92b3b48f68b255d6acc8efee1ac5682684676bba

commit 92b3b48f68b255d6acc8efee1ac5682684676bba
Author: moshayedi <moshayedi@chromium.org>
Date: Tue Mar 21 20:27:46 2017

Add system modals to the proper container in mus+ash.

System modal windows should be added to kShellWindowId_SystemModalContainer so
we get effects like gray background for them.

BUG= 702747 

Review-Url: https://codereview.chromium.org/2759643003
Cr-Commit-Position: refs/heads/master@{#458533}

[modify] https://crrev.com/92b3b48f68b255d6acc8efee1ac5682684676bba/ash/mus/window_manager.cc
[modify] https://crrev.com/92b3b48f68b255d6acc8efee1ac5682684676bba/ash/mus/window_manager.h
[modify] https://crrev.com/92b3b48f68b255d6acc8efee1ac5682684676bba/mash/simple_wm/simple_wm.cc
[modify] https://crrev.com/92b3b48f68b255d6acc8efee1ac5682684676bba/mash/simple_wm/simple_wm.h
[modify] https://crrev.com/92b3b48f68b255d6acc8efee1ac5682684676bba/services/ui/demo/mus_demo_internal.cc
[modify] https://crrev.com/92b3b48f68b255d6acc8efee1ac5682684676bba/services/ui/demo/mus_demo_internal.h
[modify] https://crrev.com/92b3b48f68b255d6acc8efee1ac5682684676bba/services/ui/test_wm/test_wm.cc
[modify] https://crrev.com/92b3b48f68b255d6acc8efee1ac5682684676bba/services/ui/ws/window_manager_client_unittest.cc
[modify] https://crrev.com/92b3b48f68b255d6acc8efee1ac5682684676bba/services/ui/ws/window_server_test_base.cc
[modify] https://crrev.com/92b3b48f68b255d6acc8efee1ac5682684676bba/services/ui/ws/window_server_test_base.h
[modify] https://crrev.com/92b3b48f68b255d6acc8efee1ac5682684676bba/ui/aura/mus/window_manager_delegate.h
[modify] https://crrev.com/92b3b48f68b255d6acc8efee1ac5682684676bba/ui/aura/mus/window_tree_client.cc
[modify] https://crrev.com/92b3b48f68b255d6acc8efee1ac5682684676bba/ui/aura/test/aura_test_base.cc
[modify] https://crrev.com/92b3b48f68b255d6acc8efee1ac5682684676bba/ui/aura/test/aura_test_base.h