Avoid a platform-specific errno in pub_serve_test.

test/runner/pub_serve_test.dart

 // Copyright (c) 2015, 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.
 
 @TestOn("vm")
 
 import 'dart:convert';
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
@@ skipping 210 matching lines @@
 Failed to load "test/my_test.dart":
 Error getting http://localhost:54321/my_test.vm_test.dart: Connection refused
 Make sure "pub serve" is running.
 '''));
     expect(result.exitCode, equals(exit_codes.data));
   });
 
   test("gracefully handles pub serve not running for browser tests", () {
     var result = runUnittest(['--pub-serve=54321', '-p', 'chrome'],
         workingDirectory: _sandbox);
-    expect(result.stderr, equals('''
-Failed to load "test/my_test.dart":
-Error getting http://localhost:54321/my_test.browser_test.dart.js: Connection refused (errno 111)
-Make sure "pub serve" is running.
+    expect(result.stderr, matches(r'''
+Failed to load "test/my_test\.dart":
+Error getting http://localhost:54321/my_test\.browser_test.dart\.js: Connection refused \(errno \d+\)
+Make sure "pub serve" is running\.
 '''));
     expect(result.exitCode, equals(exit_codes.data));
   });
 
   test("gracefully handles a test file not being in test/", () {
     new File(p.join(_sandbox, 'test/my_test.dart'))
         .copySync(p.join(_sandbox, 'my_test.dart'));
 
     var result = runUnittest(['--pub-serve=54321', 'my_test.dart'],
         workingDirectory: _sandbox);
     expect(result.stderr, equals(
         'Failed to load "my_test.dart": When using "pub serve", all test files '
             'must be in test/.\n'));
   });
 }