shill: device: export ipconfigs as object paths not strings

Export ipconfigs as object paths not strings

BUG=chromium-os:28744
TEST=run unit tests and cashew

Change-Id: I622cc69d6b6acf250ca2d7c96d0f3f0f376d4cfb
Reviewed-on: https://gerrit.chromium.org/gerrit/19528
Commit-Ready: Jason Glasgow <jglasgow@chromium.org>
Reviewed-by: Jason Glasgow <jglasgow@chromium.org>
Tested-by: Jason Glasgow <jglasgow@chromium.org>
diff --git a/device.h b/device.h
index 9e9d6ed..cd84a2a 100644
--- a/device.h
+++ b/device.h
@@ -258,6 +258,10 @@
       Strings(Device::*get)(Error *error),
       void(Device::*set)(const Strings &value, Error *error));
 
+  void HelpRegisterConstDerivedRpcIdentifiers(
+      const std::string &name,
+      RpcIdentifiers(Device::*get)(Error *));
+
   // Property getters reserved for subclasses
   ControlInterface *control_interface() const { return control_interface_; }
   Metrics *metrics() const { return metrics_; }