Eliminate explicit abstract from class members in tests

tests/standalone/io/testing_server.dart

 // Copyright (c) 2012, 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.
 
 class TestingServer {
 
   static const HOST = "127.0.0.1";
   static const INIT = 0;
   static const SHUTDOWN = -1;
 
-  abstract void onConnection(Socket connection);
+  void onConnection(Socket connection);  // Abstract.
 
   void errorHandlerServer(Exception e) {
     Expect.fail("Server socket error $e");
   }
 
   void dispatch(message, SendPort replyTo) {
     if (message == INIT) {
       _server = new ServerSocket(HOST, 0, 10);
       Expect.equals(true, _server != null);
       _server.onConnection = onConnection;
       _server.onError = errorHandlerServer;
       replyTo.send(_server.port, null);
     } else if (message == SHUTDOWN) {
       _server.close();
       port.close();
     }
   }
 
   ServerSocket _server;
 }
 
 class TestingServerTest {
 
   TestingServerTest.start(SendPort port)
       : _receivePort = new ReceivePort(),
         _sendPort = port {
     initialize();
   }
 
-  abstract void run();
+  void run();  // Abstract.
 
   void initialize() {
     _receivePort.receive((var message, SendPort replyTo) {
       _port = message;
       run();
     });
     _sendPort.send(TestingServer.INIT, _receivePort.toSendPort());
   }
 
   void shutdown() {
     _sendPort.send(TestingServer.SHUTDOWN, _receivePort.toSendPort());
     _receivePort.close();
   }
 
   int _port;
   ReceivePort _receivePort;
   SendPort _sendPort;
 }