shill: vpn: Destroy Unload()ed VPN services

BUG=chromium-os:28481
TEST=New unit test.

Change-Id: I222441d3ff5cbc7d97d97f7fdd2917eee5921721
Reviewed-on: https://gerrit.chromium.org/gerrit/19143
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Commit-Ready: Paul Stewart <pstew@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>
diff --git a/mock_vpn_service.h b/mock_vpn_service.h
index 4e6b2b1..41d8fe0 100644
--- a/mock_vpn_service.h
+++ b/mock_vpn_service.h
@@ -22,6 +22,7 @@
 
   MOCK_METHOD1(SetState, void(ConnectState state));
   MOCK_METHOD0(InitDriverPropertyStore, void());
+  MOCK_CONST_METHOD0(unloaded, bool());
 
  private:
   DISALLOW_COPY_AND_ASSIGN(MockVPNService);