Add appengine/gcloud/mustache dependencies.

pkg/appengine/lib/api/users.dart

+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library appengine.api.users;
+
+import 'dart:async';
+
+import 'package:gcloud/service_scope.dart' as ss;
+
+class User {
+  final String email;
+  final String id;
+  final String authDomain;
+  final bool isAdmin;
+
+  User({this.email, this.authDomain, this.id, this.isAdmin});
+
+  String toString() => email;
+}
+
+abstract class UserService {
+  User get currentUser;
+
+  Future<String> createLoginUrl(String destination);
+
+  Future<String> createLogoutUrl(String destination);
+}
+
+/**
+ * Register a new [UserService] object.
+ *
+ * Calling this outside of a service scope or calling it more than once inside
+ * the same service scope will result in an error.
+ *
+ * See the `package:gcloud/service_scope.dart` library for more information.
+ */
+void registerUserService(UserService service) {
+  ss.register(#_appengine.users, service);
+}
+
+/**
+ * The user service.
+ *
+ * Request handlers will be run inside a service scope which contains the
+ * users service.
+ */
+UserService get userService => ss.lookup(#_appengine.users);