Note that not working both in single-process mash and multi-process-mash.

git-bisect revealed that crrev.com/585974 causes this -- indeed looks relevant. Looking into more.

Maybe window doesn't have correct app type in mash? 

Okay, I got it. The suspected change added a check on kAppType -- which seems not set in Mash and that's why. We should fix on Mash side.

#c02 -- I missed your reply, thank you for the info!
That is true, I've created CL (https://chromium-review.googlesource.com/c/chromium/src/+/1191924) to set and propagate the property to ash -- that needs to be done for Mash and we're still missing things like this.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/14dfe4009850cd7f1c0248b0011a9cc7e7afc3bb

commit 14dfe4009850cd7f1c0248b0011a9cc7e7afc3bb
Author: Jun Mukai <mukai@chromium.org>
Date: Tue Aug 28 17:04:13 2018

set/propagate kAppType window prop for mash

A new CL requires browser windows to have kAppType window property
with AppType::BROWSER, which isn't propagated to ash yet.

Since the value enums are defined in ash/public, this property
registration is done in ash/public/cpp/window_properties.

Also, some part of ash code assumes that this property is set
on the views::Widget of ash -- which is actually the root window
of the browsers. So make it so.

Bug:  878037 
Test: manually done
Change-Id: I6da9bf77570c5bcde03df1fe0651103496b55e90
Reviewed-on: https://chromium-review.googlesource.com/1191924
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Jun Mukai <mukai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586755}
[modify] https://crrev.com/14dfe4009850cd7f1c0248b0011a9cc7e7afc3bb/ash/public/cpp/mus_property_mirror_ash.cc
[modify] https://crrev.com/14dfe4009850cd7f1c0248b0011a9cc7e7afc3bb/ash/public/cpp/window_properties.cc
[modify] https://crrev.com/14dfe4009850cd7f1c0248b0011a9cc7e7afc3bb/ash/public/interfaces/window_properties.mojom