Add additional check to vmservice/websocket_client test.

tests/standalone/vmservice/websocket_client_test.dart

 // Copyright (c) 2013, 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 unknown_command_test;
 
 import 'test_helper.dart';
 import 'package:expect/expect.dart';
 
 class ClientsRequestTest extends ServiceWebSocketRequestHelper {
   ClientsRequestTest(port) : super('ws://127.0.0.1:$port/ws');
   int _count = 0;
 
   onResponse(var seq, Map response) {
     if (seq == 'cli') {
       // Verify response is correct for 'cli' sequence id.
       Expect.equals('ClientList', response['type']);
       Expect.equals(1, response['members'].length);
       _count++;
     } else if (seq == 'vm') {
       // Verify response is correct for 'vm' sequence id.
       Expect.equals('VM', response['type']);
       _count++;
+    } else {
+      Expect.fail('Unexpected response from $seq: $response');
     }
     if (_count == 2) {
       // After receiving both responses, the test is complete.
       complete();
     }
   }
 
   runTest() {
     // Send a request for clients with 'cli' sequence id.
     sendMessage('cli', 'clients');
     // Send a request for vm info with 'vm' sequence id.
     sendMessage('vm', 'vm');
   }
 }
 
 main() {
   var process = new TestLauncher('unknown_command_script.dart');
   process.launch().then((port) {
     new ClientsRequestTest(port).connect().then((test) {
       test.completed.then((_) {
         process.requestExit();
       });
       test.runTest();
     });
   });
 }