Add Server.isClosed and Client.isClosed.

test/client/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.client.stream_test;
 
 import 'dart:async';
 
 import 'package:test/test.dart';
 import 'package:json_rpc_2/json_rpc_2.dart' as json_rpc;
@@ skipping 61 matching lines @@
     expect(() => client.listen(), throwsStateError);
   });
 
   test(".close cancels the stream subscription and closes the sink", () {
     var responseController = new StreamController();
     var requestController = new StreamController();
     var client = new json_rpc.Client(
         responseController.stream, requestController.sink);
 
     expect(client.listen(), completes);
+
+    expect(client.isClosed, isFalse);
     expect(client.close(), completes);
+    expect(client.isClosed, isTrue);
 
     expect(() => responseController.stream.listen((_) {}), throwsStateError);
     expect(requestController.isClosed, isTrue);
   });
 
   test(".close can't be called before .listen", () {
     var responseController = new StreamController();
     var requestController = new StreamController();
     var client = new json_rpc.Client(
         responseController.stream, requestController.sink);
 
     expect(() => client.close(), throwsStateError);
   });
 }