shill: Propagate Cellular errors to the DBus caller.

BUG=chromium-os:19547
TEST=unit tests

Change-Id: Ieda54d89d977a48718302c6e1e1c7927e3cf2dba
Reviewed-on: http://gerrit.chromium.org/gerrit/6603
Reviewed-by: Darin Petkov <petkov@chromium.org>
Tested-by: Darin Petkov <petkov@chromium.org>
diff --git a/service_dbus_adaptor.cc b/service_dbus_adaptor.cc
index 1b3f644..7aa801b 100644
--- a/service_dbus_adaptor.cc
+++ b/service_dbus_adaptor.cc
@@ -68,7 +68,9 @@
 }
 
 void ServiceDBusAdaptor::Connect(::DBus::Error &error) {
-  service_->Connect();
+  Error e;
+  service_->Connect(&e);
+  e.ToDBusError(&error);
 }
 
 void ServiceDBusAdaptor::Disconnect(::DBus::Error &error) {