Get mdn_ from OwnNumbers property.

Accomodate gMock's need for a value to return from modem_proxy_->OwnNumbers().

BUG=None
TEST=Manual; use list-properties and confirm that Cellular.MDN matches
the "own" number from mmcli

Change-Id: I1db04e96e2f2ddbaba958263a41a1a66be643a4d
Reviewed-on: https://gerrit.chromium.org/gerrit/20256
Tested-by: Nathan J. Williams <njw@chromium.org>
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Commit-Ready: Nathan J. Williams <njw@chromium.org>
diff --git a/cellular_capability_universal_unittest.cc b/cellular_capability_universal_unittest.cc
index c19f14c..8160102 100644
--- a/cellular_capability_universal_unittest.cc
+++ b/cellular_capability_universal_unittest.cc
@@ -4,6 +4,9 @@
 
 #include "shill/cellular_capability_universal.h"
 
+#include <string>
+#include <vector>
+
 #include <base/bind.h>
 #include <chromeos/dbus/service_constants.h>
 #include <gtest/gtest.h>
@@ -30,6 +33,7 @@
 using base::Bind;
 using base::Unretained;
 using std::string;
+using std::vector;
 using testing::InSequence;
 using testing::NiceMock;
 using testing::Return;
@@ -173,6 +177,7 @@
   EXPECT_CALL(*modem_3gpp_proxy_, Imei()).WillOnce(Return(kImei));
   EXPECT_CALL(*modem_3gpp_proxy_, RegistrationState())
       .WillOnce(Return(MM_MODEM_3GPP_REGISTRATION_STATE_UNKNOWN));
+  EXPECT_CALL(*modem_proxy_, OwnNumbers()).WillOnce(Return(vector<string>()));
 
   // After setup we lose pointers to the proxies, so it is hard to set
   // expectations.