Make event-handlers edge-triggered and move socket-state to Dart.

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 {
@@ skipping 28 matching lines @@
 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();
     });
   });
-}
+}