Add Server.isClosed and Client.isClosed.

test/server/stream_test.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 json_rpc_2.test.server.stream_test;
 
 import 'dart:async';
 
 import 'package:test/test.dart';
 import 'package:json_rpc_2/json_rpc_2.dart' as json_rpc;
@@ skipping 63 matching lines @@
     expect(() => server.listen(), throwsStateError);
   });
 
   test(".close cancels the stream subscription and closes the sink", () {
     var requestController = new StreamController();
     var responseController = new StreamController();
     var server = new json_rpc.Server(
         requestController.stream, responseController.sink);
 
     expect(server.listen(), completes);
+
+    expect(server.isClosed, isFalse);
     expect(server.close(), completes);
+    expect(server.isClosed, isTrue);
 
     expect(() => requestController.stream.listen((_) {}), throwsStateError);
     expect(responseController.isClosed, isTrue);
   });
 
   test(".close can't be called before .listen", () {
     var requestController = new StreamController();
     var responseController = new StreamController();
     var server = new json_rpc.Server(
         requestController.stream, responseController.sink);
 
     expect(() => server.close(), throwsStateError);
   });
 }