shill: vpn: Load and save OpenVPN service properties.

BUG=chromium-os:27650
TEST=unit tests

Change-Id: If620f34ecbf82be018b546c290e3fa1baa6fc001
Reviewed-on: https://gerrit.chromium.org/gerrit/18650
Tested-by: Darin Petkov <petkov@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Ready: Darin Petkov <petkov@chromium.org>
diff --git a/vpn_service.h b/vpn_service.h
index a004cc7..203357f 100644
--- a/vpn_service.h
+++ b/vpn_service.h
@@ -28,6 +28,8 @@
   virtual void Connect(Error *error);
   virtual void Disconnect(Error *error);
   virtual std::string GetStorageIdentifier() const;
+  virtual bool Load(StoreInterface *storage);
+  virtual bool Save(StoreInterface *storage);
 
   VPNDriver *driver() const { return driver_.get(); }