Implement support for monitor suspend.

chromeos/dbus/power_manager_client.h

Index: chromeos/dbus/power_manager_client.h
diff --git a/chromeos/dbus/power_manager_client.h b/chromeos/dbus/power_manager_client.h
index 70ac0da0eaf3842e510082f15c87f2306c035ef5..4a649025e649c465472be17260c2ece4177772b8 100644
--- a/chromeos/dbus/power_manager_client.h
+++ b/chromeos/dbus/power_manager_client.h
@@ -67,6 +67,10 @@ class CHROMEOS_EXPORT PowerManagerClient {
     // (as opposed to the more-common method of adjusting the backlight).
     virtual void ScreenDimmingRequested(ScreenDimmingState state) {}
 
+    // Called when the system is about to suspend. Suspend is deferred until
+    // all observers' implementations of this method have finished running.
+    virtual void SuspendImminent() {}
+
     // Called when the power button is pressed or released.
     // Note: Implement both this method and
     // RootPowerManagerObserver::OnPowerButtonEvent() until this has been moved