I could see making two targets, where things like DeviceDataManager/DeviceHotplugEventObserver/etc. should be not used in ash/chrome. The other half, InputDeviceManager/InputDevice/TouchscreenDevice/etc. is more client-y code though?

Excellent idea!

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b840aa23c0d85adeadb283a6d41108015756d5f7

commit b840aa23c0d85adeadb283a6d41108015756d5f7
Author: James Cook <jamescook@chromium.org>
Date: Thu Oct 26 19:40:29 2017

cros: Fix ash_unittests --mus for TrayIME and VirtualKeyboardController

They were using ui::DeviceDataManager, which does not exist in mus.

Switch tests to use ui::InputDeviceManager and add test support methods.
I can't add an InputDeviceManagerTestApi because there are two different
concrete implementations.

Tighten DEPS restrictions for DeviceDataManager.

Bug: 745005,  747415 
Test: ash_unittests --mus
Change-Id: Ia3e250218888bda7f45d199575852979a568ad2c
Reviewed-on: https://chromium-review.googlesource.com/738850
Commit-Queue: James Cook <jamescook@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#511926}
[modify] https://crrev.com/b840aa23c0d85adeadb283a6d41108015756d5f7/ash/DEPS
[modify] https://crrev.com/b840aa23c0d85adeadb283a6d41108015756d5f7/ash/display/DEPS
[modify] https://crrev.com/b840aa23c0d85adeadb283a6d41108015756d5f7/ash/system/ime/tray_ime_chromeos_unittest.cc
[modify] https://crrev.com/b840aa23c0d85adeadb283a6d41108015756d5f7/ash/virtual_keyboard_controller_unittest.cc
[modify] https://crrev.com/b840aa23c0d85adeadb283a6d41108015756d5f7/services/ui/public/cpp/input_devices/input_device_client.cc
[modify] https://crrev.com/b840aa23c0d85adeadb283a6d41108015756d5f7/services/ui/public/cpp/input_devices/input_device_client.h
[modify] https://crrev.com/b840aa23c0d85adeadb283a6d41108015756d5f7/testing/buildbot/filters/ash_unittests_mash.filter
[modify] https://crrev.com/b840aa23c0d85adeadb283a6d41108015756d5f7/testing/buildbot/filters/ash_unittests_mus.filter
[modify] https://crrev.com/b840aa23c0d85adeadb283a6d41108015756d5f7/ui/events/devices/device_data_manager.cc
[modify] https://crrev.com/b840aa23c0d85adeadb283a6d41108015756d5f7/ui/events/devices/device_data_manager.h
[modify] https://crrev.com/b840aa23c0d85adeadb283a6d41108015756d5f7/ui/events/devices/input_device_manager.h