Is this a FileManager-specific bug? Removing the FileManager component because I think this is a bug that would affect all custom-frame Chrome Apps.

This still repros and is probably applicable to all custom-frame containers.

Scott mentioned that this is probably an issue with the frame's non-client area. Ash is probably rendering the caption buttons, and so Ash should get events for those views, but the app is getting the events instead.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1145abadfce5c466cdff408925707a99a0d24a89

commit 1145abadfce5c466cdff408925707a99a0d24a89
Author: Evan Stade <estade@chromium.org>
Date: Tue Apr 24 14:09:08 2018

Mash: fix colored app window frames.

Previously, in Mash, Ash used an EmptyDraggableNonClientFrameView and
Chrome drew an AppWindowFrameView on top of that. Events went to the
former, which didn't know about caption buttons, and AppWindowFrameView
draws Windows-style caption buttons, so both appearance and behavior
were broken. (In classic Ash, Chrome uses a CustomFrameViewAsh.)

Now, in Mash, Chrome doesn't have a NonClientFrameView, but tells Ash
about the frame's colors via mus init properties. The Ash-process
CustomFrameViewAsh will be painted correctly and be able to handle
events.

Bug:  766712 
Change-Id: Ic272e5755d0ac9af325b512bb0c3ccbe87fcb2c8
Reviewed-on: https://chromium-review.googlesource.com/1023036
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553088}
[modify] https://crrev.com/1145abadfce5c466cdff408925707a99a0d24a89/ash/wm/non_client_frame_controller.cc
[modify] https://crrev.com/1145abadfce5c466cdff408925707a99a0d24a89/ash/wm/property_util.cc
[modify] https://crrev.com/1145abadfce5c466cdff408925707a99a0d24a89/ash/wm/property_util.h
[modify] https://crrev.com/1145abadfce5c466cdff408925707a99a0d24a89/chrome/browser/ui/views/apps/chrome_native_app_window_views.cc
[modify] https://crrev.com/1145abadfce5c466cdff408925707a99a0d24a89/chrome/browser/ui/views/apps/chrome_native_app_window_views.h
[modify] https://crrev.com/1145abadfce5c466cdff408925707a99a0d24a89/chrome/browser/ui/views/apps/chrome_native_app_window_views_aura_ash.cc
[modify] https://crrev.com/1145abadfce5c466cdff408925707a99a0d24a89/chrome/browser/ui/views/apps/chrome_native_app_window_views_aura_ash.h
[modify] https://crrev.com/1145abadfce5c466cdff408925707a99a0d24a89/services/ui/public/interfaces/window_manager.mojom