Create watch list for messages.yaml.

WATCHLISTS

Index: WATCHLISTS
diff --git a/WATCHLISTS b/WATCHLISTS
index c626ed4cf695bfc12c53a23d75675df417b98de0..32e07369d25f7d9aa17f9fe27aad5a9fc4472eaf 100644
--- a/WATCHLISTS
+++ b/WATCHLISTS
@@ -19,12 +19,16 @@
     },
     'front_end': {
       'filepath': '^pkg/front_end',
-    }
+    },
+    'messages_review': {
+      'filepath': '^pkg/front_end/messages.yaml',
+    },
   },
 
   'WATCHLISTS': {
     'runtime': ['vm-dev@dartlang.org'],
     'observatory': ['johnmccutchan@google.com', 'turnidge@google.com', 'rmacnak@google.com'],
     'front_end': ['dart-fe-team+reviews@google.com'],
+    'messages_review': [ 'dart-uxr+reviews@google.com' ],
   },
 }