Add Observatory test of io.

tests/standalone/io/socket_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.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 
 import "dart:async";
 import "dart:io";
 
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 
 void testArguments() {
   Expect.throws(() => ServerSocket.bind("127.0.0.1", 65536));
   Expect.throws(() => ServerSocket.bind("127.0.0.1", -1));
   Expect.throws(() => ServerSocket.bind("127.0.0.1", 0, backlog: -1));
 }
 
 void testSimpleBind() {
   asyncStart();
   ServerSocket.bind(InternetAddress.LOOPBACK_IP_V4, 0).then((s) {
     Expect.isTrue(s.port > 0);
+    s.close();
     asyncEnd();
   });
 }
 
 void testInvalidBind() {
   // Bind to a unknown DNS name.
   asyncStart();
   ServerSocket.bind("ko.faar.__hest__", 0)
       .then((_) { Expect.fail("Failure expected"); } )
       .catchError((error) {
@@ skipping 169 matching lines @@
   testInvalidBind();
   testConnectImmediateDestroy();
   testConnectConsumerClose();
   testConnectConsumerWriteClose();
   testConnectStreamClose();
   testConnectStreamDataClose(true);
   testConnectStreamDataClose(false);
   testConnectStreamDataCloseCancel(true);
   testConnectStreamDataCloseCancel(false);
 }