power_manager: Add [S,G]etBacklightsForcedOff constants.

Add constants for new SetBacklightsForcedOff and
GetBacklightsForcedOff D-Bus methods that will be exported
by powerd.

BUG=chromium:651669
TEST=built it

Change-Id: Id4724935fe9e5352feea4cc535d6c5a52acd2dc9
Reviewed-on: https://chromium-review.googlesource.com/394146
Commit-Ready: Dan Erat <derat@chromium.org>
Tested-by: Dan Erat <derat@chromium.org>
Reviewed-by: Qiang Xu <warx@chromium.org>
Reviewed-by: Eric Caruso <ejcaruso@chromium.org>
diff --git a/dbus/power_manager/dbus-constants.h b/dbus/power_manager/dbus-constants.h
index fa42cb1..0a3dfac 100644
--- a/dbus/power_manager/dbus-constants.h
+++ b/dbus/power_manager/dbus-constants.h
@@ -26,6 +26,8 @@
 const char kSetIsProjectingMethod[] = "SetIsProjecting";
 const char kSetPolicyMethod[] = "SetPolicy";
 const char kSetPowerSourceMethod[] = "SetPowerSource";
+const char kSetBacklightsForcedOffMethod[] = "SetBacklightsForcedOff";
+const char kGetBacklightsForcedOffMethod[] = "GetBacklightsForcedOff";
 const char kRegisterSuspendDelayMethod[] = "RegisterSuspendDelay";
 const char kUnregisterSuspendDelayMethod[] = "UnregisterSuspendDelay";
 const char kHandleSuspendReadinessMethod[] = "HandleSuspendReadiness";