[shill] Add support for setting properties.

This CL adds a framework for supporting RPC-exposed properties in Shill.
It also plumbs the code for setting properties on Service objects to prove
the approach.  Device and Manager settings will follow.

BUG=chromium-os:16343
TEST=build shill, run unit tests.

Change-Id: I55869453d6039e688f1a49be9dfb1ba1315efe0a
Reviewed-on: http://gerrit.chromium.org/gerrit/3004
Reviewed-by: Darin Petkov <petkov@chromium.org>
Tested-by: Chris Masone <cmasone@chromium.org>
diff --git a/ethernet_service.h b/ethernet_service.h
index 9478691..1886854 100644
--- a/ethernet_service.h
+++ b/ethernet_service.h
@@ -26,8 +26,13 @@
   ~EthernetService();
   void Connect();
   void Disconnect();
+
+ protected:
+  virtual std::string CalculateState() { return "idle"; }
+
  private:
   Ethernet *ethernet_;
+  const std::string type_;
   DISALLOW_COPY_AND_ASSIGN(EthernetService);
 };