shill: vpn: Disconnect VPN service when underlying connection disconnects.

BUG=chromium-os:30737,chromium-os:30774
TEST=unit tests, tested on device with 000OpenVPNGenesis

Change-Id: Ib350cb23edd3e68b3bd5390378789a6b60857b80
Reviewed-on: https://gerrit.chromium.org/gerrit/22461
Tested-by: Darin Petkov <petkov@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Commit-Ready: Darin Petkov <petkov@chromium.org>
diff --git a/connection_unittest.cc b/connection_unittest.cc
index 4154373..a1fda3b 100644
--- a/connection_unittest.cc
+++ b/connection_unittest.cc
@@ -28,7 +28,6 @@
 using testing::_;
 using testing::NiceMock;
 using testing::Return;
-using testing::ReturnRef;
 using testing::StrictMock;
 using testing::Test;
 
@@ -609,6 +608,7 @@
     connection = NULL;
 
     // Ensure no crash -- the weak pointer to connection should be NULL.
+    EXPECT_FALSE(binder.connection());
     binder.Attach(NULL);
   }
 }