Add appengine/gcloud/mustache dependencies.

pkg/appengine/lib/src/protobuf_api/rpc/rpc_service.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 rpc_service;
+
+import 'dart:async';
+
+class RpcApplicationError implements Exception {
+  final int code;
+  final String message;
+
+  RpcApplicationError(this.code, this.message);
+  String toString() => 'RpcApplicationError: $code ($message)';
+}
+
+abstract class RPCService {
+  Future<List<int>> call(String apiPackage,
+                         String method,
+                         List<int> requestProtocolBuffer,
+                         {String ticket: 'invalid-ticket'});
+}