shill: Propagate Cellular Activate call errors to the DBus caller.

BUG=chromium-os:19547
TEST=unit tests

Change-Id: I2a0f889f0863c299c3f3ac006a6df5a608407881
Reviewed-on: http://gerrit.chromium.org/gerrit/6616
Reviewed-by: Darin Petkov <petkov@chromium.org>
Tested-by: Darin Petkov <petkov@chromium.org>
diff --git a/cellular_service.cc b/cellular_service.cc
index 471ad4c..a6c1140 100644
--- a/cellular_service.cc
+++ b/cellular_service.cc
@@ -51,8 +51,9 @@
 
 void CellularService::Disconnect() { }
 
-void CellularService::ActivateCellularModem(const string &carrier) {
-  cellular_->Activate(carrier);
+void CellularService::ActivateCellularModem(const string &carrier,
+                                            Error *error) {
+  cellular_->Activate(carrier, error);
 }
 
 string CellularService::GetStorageIdentifier(const string &mac) {