Add dark resume methods to PowerManagerClient

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 f37476e0127202e90ccfdb35c93a9f45ba0984b1..e9e1d00f105c44dde2e11f7960b0b03fc319bad7 100644
--- a/chromeos/dbus/power_manager_client.h
+++ b/chromeos/dbus/power_manager_client.h
@@ -71,6 +71,14 @@ class CHROMEOS_EXPORT PowerManagerClient : public DBusClient {
     // suspended (if e.g. the user canceled the suspend attempt).
     virtual void SuspendDone(const base::TimeDelta& sleep_duration) {}
 
+    // Called when the system is about to resuspend from a dark resume.  Like
+    // SuspendImminent(), the suspend will be deferred until all observers have
+    // finished running and those observers that wish to asynchromously delay
+    // the suspend should call PowerManagerClient::GetSuspendReadinessCallback()
+    // from within this method.  The returned callback should be run once the
+    // observer is ready for suspend.

[Daniel Erat, 2014/08/18 21:02:13]

i embarrassingly forgot how this interface works and thought that observers
would call GetSuspendReadinessCallback() once when they registered themselves
instead of in the middle of a *SuspendImminent() call.

this still seems problematic to me, though -- isn't there now a hidden
dependency that the two ID sequences never overlap lest one late asynchronous
callback accidentally ack a different suspend attempt than the one it was
originally invoked for?

one simple, albeit maybe hacky, way to avoid this would be to also bind a
parameter to the callbacks specifying whether they were generated in response to
regular suspend attempts or dark suspend attempts and then check that it lines
up with the current attempt when the callback is invoked.

[Chirantan Ekbote, 2014/08/18 21:15:43]

True, but with the way powerd generates IDs we would need 2^15 suspend attempts
and 0 dark suspend attempts before the two IDs would risk overlapping.
sgtm.  We can bind the value of suspending_from_dark_resume_ and then check it
when the callback is run.

+    virtual void DarkSuspendImminent() {}
+
     // Called when the power button is pressed or released.
     virtual void PowerButtonEventReceived(bool down,
                                           const base::TimeTicks& timestamp) {}