I'm investigating short-term approaches for forwarding user activity from UserActivityMonitor to ui::UserActivityDetector without needing to update all of the existing code that uses ui::UserActivityObserver.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/94887a2c9af708195be7560415090dd70eabd049

commit 94887a2c9af708195be7560415090dd70eabd049
Author: derat <derat@chromium.org>
Date: Fri Jan 20 18:17:25 2017

mus: Forward user activity from window server to detector.

Introduce an aura::UserActivityForwarder class that
receives reports of user activity from the window server via
mojo and forwards them to ui::UserActivityDetector so that
existing classes implementing ui::UserActivityObserver will
be notified.

This results in user activity being reported to the Chrome
OS power manager to prevent the display from being dimmed
and turned off.

BUG=626899

Review-Url: https://codereview.chromium.org/2639703004
Cr-Commit-Position: refs/heads/master@{#445095}

[modify] https://crrev.com/94887a2c9af708195be7560415090dd70eabd049/ash/shell.cc
[modify] https://crrev.com/94887a2c9af708195be7560415090dd70eabd049/ash/shell.h
[modify] https://crrev.com/94887a2c9af708195be7560415090dd70eabd049/services/ui/manifest.json
[modify] https://crrev.com/94887a2c9af708195be7560415090dd70eabd049/ui/aura/BUILD.gn
[modify] https://crrev.com/94887a2c9af708195be7560415090dd70eabd049/ui/aura/mus/DEPS
[add] https://crrev.com/94887a2c9af708195be7560415090dd70eabd049/ui/aura/mus/user_activity_forwarder.cc
[add] https://crrev.com/94887a2c9af708195be7560415090dd70eabd049/ui/aura/mus/user_activity_forwarder.h
[add] https://crrev.com/94887a2c9af708195be7560415090dd70eabd049/ui/aura/mus/user_activity_forwarder_unittest.cc
[modify] https://crrev.com/94887a2c9af708195be7560415090dd70eabd049/ui/aura/test/DEPS
[modify] https://crrev.com/94887a2c9af708195be7560415090dd70eabd049/ui/aura/test/run_all_unittests.cc
[modify] https://crrev.com/94887a2c9af708195be7560415090dd70eabd049/ui/base/user_activity/user_activity_detector.cc
[modify] https://crrev.com/94887a2c9af708195be7560415090dd70eabd049/ui/base/user_activity/user_activity_detector.h
[modify] https://crrev.com/94887a2c9af708195be7560415090dd70eabd049/ui/base/user_activity/user_activity_detector_unittest.cc
[modify] https://crrev.com/94887a2c9af708195be7560415090dd70eabd049/ui/chromeos/user_activity_power_manager_notifier.h

We'll also need to instantiate ui::UserActivityDetector, ui::UserActivityPowerManagerNotifier, and ui::UserActivityForwarder in Chrome-on-mus. Right now, all three are instantiated by ash::Shell (the latter only for mash).

Much longer term, when mus is always available, classes that care about user activity/idleness should register themselves as observers of the UserActivityMonitor ws interface and receive notifications directly. Then UserActivityDetector and UserActivityForwarder can be removed.

This is still relevant, but only for multi-process mash.

Dan, re: comment 7, "mus" is now always available. (Code in //ash always provides the window service mojo APIs via //services/ui/ws2.) The "window service process" and "ash process" are now the same process. Could that simplify things?

(This came up while looking at ChromeBrowserMainExtraPartsAsh::PreProfileInit() today.)

I'm unlikely to get to this in the near future, so marking it as up for grabs.