buffet: Add an XMPP client class

This is a relatively simple XMPP client class, which at this point,
is only used to keep the XMPP connection open to GCD.

TEST=FEATURES=test emerge buffet
BUG=brillo:95

Change-Id: I2e7c8d7352892bd7c94e630cc7872f32f2298ae4
Reviewed-on: https://chromium-review.googlesource.com/248351
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Nathan Bullock <nathanbullock@google.com>
Tested-by: Nathan Bullock <nathanbullock@google.com>
diff --git a/buffet/buffet.gyp b/buffet/buffet.gyp
index d4c4541..6628f4d 100644
--- a/buffet/buffet.gyp
+++ b/buffet/buffet.gyp
@@ -43,6 +43,8 @@
         'states/state_manager.cc',
         'states/state_package.cc',
         'utils.cc',
+        'xmpp/xmpp_client.cc',
+        'xmpp/xmpp_connection.cc',
       ],
       'includes': ['../common-mk/generate-dbus-adaptors.gypi'],
       'actions': [
@@ -117,6 +119,7 @@
             'states/state_change_queue_unittest.cc',
             'states/state_manager_unittest.cc',
             'states/state_package_unittest.cc',
+            'xmpp/xmpp_client_unittest.cc',
           ],
         },
       ],