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/ethernet_service.h b/ethernet_service.h
index adcc0eb..d0dbf0b 100644
--- a/ethernet_service.h
+++ b/ethernet_service.h
@@ -24,8 +24,10 @@
                   Manager *manager,
                   const EthernetRefPtr &device);
   ~EthernetService();
-  void Connect();
-  void Disconnect();
+
+  // Inherited from Service.
+  virtual void Connect(Error *error);
+  virtual void Disconnect();
 
   // ethernet_<MAC>
   virtual std::string GetStorageIdentifier(const std::string &mac);