update_engine: Pass reboot description to powerd.

Make update_engine pass a description of why it's requesting
a reboot to the Chrome OS power manager.

BUG=chromium:762328
TEST=built with FEATURES=test
CQ-DEPEND=Ifcfcdde0df20e8e341e8aa9bc0002b10c56cd5e7

Change-Id: Ia5c6eb1705902dd8f87de701f4ee15fc3b389a3d
Reviewed-on: https://chromium-review.googlesource.com/658609
Commit-Ready: Dan Erat <derat@chromium.org>
Tested-by: Dan Erat <derat@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
diff --git a/power_manager_chromeos.cc b/power_manager_chromeos.cc
index e175f95..23fb032 100644
--- a/power_manager_chromeos.cc
+++ b/power_manager_chromeos.cc
@@ -16,6 +16,8 @@
 
 #include "update_engine/power_manager_chromeos.h"
 
+#include <memory>
+
 #include <power_manager/dbus-constants.h>
 #include <power_manager/dbus-proxies.h>
 
@@ -37,7 +39,9 @@
             << ::power_manager::kRequestRestartMethod;
   brillo::ErrorPtr error;
   return power_manager_proxy_.RequestRestart(
-      ::power_manager::REQUEST_RESTART_FOR_UPDATE, &error);
+      ::power_manager::REQUEST_RESTART_FOR_UPDATE,
+      "update_engine applying update",
+      &error);
 }
 
 }  // namespace chromeos_update_engine