shill: make Connectable property of WiFiService reflect state
of security requirements and available credentials

BUG=chromium-os:23352
TEST=new unittests

Change-Id: I3d98512073d2280a40eee3fd462f592c43df00f3
Reviewed-on: https://gerrit.chromium.org/gerrit/12093
Tested-by: mukesh agrawal <quiche@chromium.org>
Reviewed-by: Gaurav Shah <gauravsh@chromium.org>
Commit-Ready: mukesh agrawal <quiche@chromium.org>
diff --git a/wifi_service.h b/wifi_service.h
index fb9377a..113673f 100644
--- a/wifi_service.h
+++ b/wifi_service.h
@@ -80,6 +80,7 @@
   void ConnectTask();
 
   std::string GetDeviceRpcId(Error *error);
+  void UpdateConnectable();
 
   static void ValidateWEPPassphrase(const std::string &passphrase,
                                     Error *error);