Support in update_engine for script for UI jank investigation.

We need to update image_to_live.sh to run in a loop to help investigate
the kernel behavior during AU. Since update_engine doesn't allow a
new update to be applied unless the device is rebooted after the previous
update, this CL adds an option to reset the state for testing purposes.

This CL does not cause any change in product code, since
update_engine_client will never be invoked with this option in product.

BUG=chromium-os:27954
TEST=Tested on ZGB.
Change-Id: I561e58893818a1b4990fdc131cd3bb64e473155e
Reviewed-on: https://gerrit.chromium.org/gerrit/29907
Commit-Ready: Jay Srinivasan <jaysri@chromium.org>
Reviewed-by: Jay Srinivasan <jaysri@chromium.org>
Tested-by: Jay Srinivasan <jaysri@chromium.org>
diff --git a/dbus_service.cc b/dbus_service.cc
index ef68596..2d0f31b 100644
--- a/dbus_service.cc
+++ b/dbus_service.cc
@@ -100,6 +100,13 @@
   return TRUE;
 }
 
+gboolean update_engine_service_reset_status(UpdateEngineService* self,
+                                            GError **error) {
+  *error = NULL;
+  return self->update_attempter_->ResetStatus();
+}
+
+
 gboolean update_engine_service_get_status(UpdateEngineService* self,
                                           int64_t* last_checked_time,
                                           double* progress,