buffet: Start XMPP immediately after registration

TEST=manually and FEATURES=test emerge-${BOARD} buffet
BUG=brillo:287

Change-Id: I26f59e2b12a6ca5b49569efd7495e920e58aefe5
Reviewed-on: https://chromium-review.googlesource.com/251045
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Nathan Bullock <nathanbullock@google.com>
Commit-Queue: Nathan Bullock <nathanbullock@google.com>
Tested-by: Nathan Bullock <nathanbullock@google.com>
diff --git a/buffet/device_registration_info.h b/buffet/device_registration_info.h
index 046ba7f..7046718 100644
--- a/buffet/device_registration_info.h
+++ b/buffet/device_registration_info.h
@@ -143,6 +143,10 @@
   // Makes sure the access token is available and up-to-date.
   bool ValidateAndRefreshAccessToken(chromeos::ErrorPtr* error);
 
+  // This attempts to open the XMPP channel. The XMPP channel needs to be
+  // restarted anytime the access_token is refreshed.
+  void StartXmpp();
+
   using CloudRequestCallback =
       base::Callback<void(const base::DictionaryValue&)>;
   using CloudRequestErrorCallback =