shill: add property change notifications for IPConfig objects

Chrome monitors the kAddressProperty and the kNameServersProperty.
So emit changes for them.

BUG=chromium:230329
TEST=new unit tests

Change-Id: I0015441f62152d3d4c51a46bd95ff73acbf16def
Reviewed-on: https://gerrit.chromium.org/gerrit/48916
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Queue: mukesh agrawal <quiche@chromium.org>
Tested-by: mukesh agrawal <quiche@chromium.org>
diff --git a/mock_adaptors.h b/mock_adaptors.h
index a454b65..014370d 100644
--- a/mock_adaptors.h
+++ b/mock_adaptors.h
@@ -54,6 +54,8 @@
   MOCK_METHOD2(EmitUintChanged, void(const std::string&, uint32));
   MOCK_METHOD2(EmitIntChanged, void(const std::string&, int));
   MOCK_METHOD2(EmitStringChanged, void(const std::string&, const std::string&));
+  MOCK_METHOD2(EmitStringsChanged,
+               void(const std::string&, const std::vector<std::string>&));
 
  private:
   const std::string rpc_id_;