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/cellular_service.h b/cellular_service.h
index 7224774..895a146 100644
--- a/cellular_service.h
+++ b/cellular_service.h
@@ -29,7 +29,7 @@
   virtual ~CellularService();
 
   // Inherited from Service.
-  virtual void Connect();
+  virtual void Connect(Error *error);
   virtual void Disconnect();
   virtual void ActivateCellularModem(const std::string &carrier);