Use the polling watcher by default in pub tests for now.

sdk/lib/_internal/pub/test/serve/invalid_urls_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.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 pub_tests;
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 import 'utils.dart';
 
@@ skipping 18 matching lines @@
         d.file("packages"),
         d.file("assets")
       ]),
       d.dir("web", [
         d.file("packages"),
         d.file("assets")
       ])
     ]).create();
 
     pubGet();
-    startPubServe();
+    pubServe();
     requestShould404("packages");
     requestShould404("assets");
     requestShould404("packages/");
     requestShould404("assets/");
     requestShould404("packages/myapp");
     requestShould404("assets/myapp");
     requestShould404("packages/myapp/");
     requestShould404("assets/myapp/");
     requestShould404("packages/foo");
     requestShould404("assets/foo");
     requestShould404("packages/foo/");
     requestShould404("assets/foo/");
     requestShould404("packages/unknown");
     requestShould404("assets/unknown");
     requestShould404("packages/unknown/");
     requestShould404("assets/unknown/");
     endPubServe();
   });
 
 }