I think we probably need a method that returns the current delays, after all. It looks like there are cases where the delays don't change when Chrome is restarted (but the restarted Chrome process still needs some way to get them).

Sent https://crrev.com/c/862985 and https://crrev.com/c/862991 for the OS part of this.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/platform2/+/15e2d0b8f139d2a8fc51d528425eae26f1e7338a

commit 15e2d0b8f139d2a8fc51d528425eae26f1e7338a
Author: Daniel Erat <derat@chromium.org>
Date: Fri Jan 12 11:27:13 2018

power: Emit InactivityDelaysChanged D-Bus signals.

Make powerd emit an InactivityDelaysChanged D-Bus signal
containing a serialized PowerManagementPolicy::Delays
protocol buffer whenever the current inactivity delays
change, and add a GetInactivityDelays method that can be
called to get the current delays.

Also add the existing ScreenIdleStateChanged signal to
org.chromium.PowerManager.xml (although its only consumer is
Chrome, which doesn't use generated D-Bus bindings).

BUG= chromium:801177 
TEST=added unit tests; also manually observed with:
     dbus-monitor --system "member='InactivityDelaysChanged'"
     and queried with:
     dbus-send --system --dest=org.chromium.PowerManager \
       --print-reply --type=method_call \
       /org/chromium/PowerManager \
       org.chromium.PowerManager.GetInactivityDelays
CQ-DEPEND=I5f39d47f42b504c5c18238182a093f0abf072d98

Change-Id: Ie8e536de37694b6c096e073e570a1ad1634b139f
Reviewed-on: https://chromium-review.googlesource.com/862991
Commit-Ready: Dan Erat <derat@chromium.org>
Tested-by: Dan Erat <derat@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>

[modify] https://crrev.com/15e2d0b8f139d2a8fc51d528425eae26f1e7338a/wimax_manager/power_manager_dbus_proxy.h
[modify] https://crrev.com/15e2d0b8f139d2a8fc51d528425eae26f1e7338a/power_manager/powerd/policy/state_controller_unittest.cc
[modify] https://crrev.com/15e2d0b8f139d2a8fc51d528425eae26f1e7338a/power_manager/powerd/daemon.cc
[modify] https://crrev.com/15e2d0b8f139d2a8fc51d528425eae26f1e7338a/power_manager/powerd/policy/state_controller.h
[modify] https://crrev.com/15e2d0b8f139d2a8fc51d528425eae26f1e7338a/power_manager/powerd/daemon.h
[modify] https://crrev.com/15e2d0b8f139d2a8fc51d528425eae26f1e7338a/power_manager/dbus_bindings/org.chromium.PowerManager.xml
[modify] https://crrev.com/15e2d0b8f139d2a8fc51d528425eae26f1e7338a/power_manager/powerd/policy/state_controller.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/platform/system_api/+/9f0f93fcd84696cb278ef79538bb346345cab648

commit 9f0f93fcd84696cb278ef79538bb346345cab648
Author: Daniel Erat <derat@chromium.org>
Date: Fri Jan 12 11:27:12 2018

system_api: Add powerd inactivity delays signal and method.

Add a constant for a new InactivityDelaysChanged D-Bus
signal containing a serialized PowerManagementPolicy::Delays
protocol buffer that powerd will emit when its delays
change.

Also add a GetInactivityDelays method that can be called to
get the current delays (again, as a Delays protobuf).

BUG= chromium:801177 
TEST=emerged system-api

Change-Id: I5f39d47f42b504c5c18238182a093f0abf072d98
Reviewed-on: https://chromium-review.googlesource.com/862985
Commit-Ready: Dan Erat <derat@chromium.org>
Tested-by: Dan Erat <derat@chromium.org>
Reviewed-by: Eric Caruso <ejcaruso@chromium.org>

[modify] https://crrev.com/9f0f93fcd84696cb278ef79538bb346345cab648/dbus/power_manager/dbus-constants.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5b3be9c08b5a6af4990f52c01b64f8b9c8febfd8

commit 5b3be9c08b5a6af4990f52c01b64f8b9c8febfd8
Author: Daniel Erat <derat@chromium.org>
Date: Wed Jan 17 03:15:36 2018

Roll src/third_party/cros_system_api/ 9efc03a3d..15e1a4681 (4 commits)

https://chromium.googlesource.com/chromiumos/platform/system_api.git/+log/9efc03a3dca4..15e1a468124f

$ git log 9efc03a3d..15e1a4681 --date=short --no-merges --format='%ad %ae %s'
2018-01-02 maybelle shill: Add EAP.UseLoginPassword constant.
2018-01-02 khmel arc: Extend StartArcInstanceRequest for skip_packages_cache_setup
2018-01-11 derat system_api: Add powerd inactivity delays signal and method.
2018-01-08 ejcaruso shill: add Cellular.EquipmentID property

Created with:
  roll-dep src/third_party/cros_system_api

Bug:  801177 
Change-Id: I508a8b6fd19c7a38464ebba98a9b93bcecf866d0
Reviewed-on: https://chromium-review.googlesource.com/867093
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Dan Erat <derat@chromium.org>
Cr-Commit-Position: refs/heads/master@{#529564}
[modify] https://crrev.com/5b3be9c08b5a6af4990f52c01b64f8b9c8febfd8/DEPS

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/62b3c19c350daa306b32d77235d77ac3bab4889d

commit 62b3c19c350daa306b32d77235d77ac3bab4889d
Author: Daniel Erat <derat@chromium.org>
Date: Wed Jan 17 06:17:41 2018

chromeos: Handle inactivity delays in PowerManagerClient.

Update chromeos::PowerManagerClient to listen for
InactivityDelaysChanged D-Bus signals from powerd and
support calling powerd's GetInactivityDelays method.

Bug:  801177 
Change-Id: Ib9ea85ef33c9483185040a749864dc7b88c76933
Reviewed-on: https://chromium-review.googlesource.com/867390
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Dan Erat <derat@chromium.org>
Cr-Commit-Position: refs/heads/master@{#529651}
[modify] https://crrev.com/62b3c19c350daa306b32d77235d77ac3bab4889d/chromeos/dbus/fake_power_manager_client.cc
[modify] https://crrev.com/62b3c19c350daa306b32d77235d77ac3bab4889d/chromeos/dbus/fake_power_manager_client.h
[modify] https://crrev.com/62b3c19c350daa306b32d77235d77ac3bab4889d/chromeos/dbus/power_manager_client.cc
[modify] https://crrev.com/62b3c19c350daa306b32d77235d77ac3bab4889d/chromeos/dbus/power_manager_client.h