Fix static warning in test:

tests/isolate/package_root_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.
 
 import 'dart:io';
 import 'dart:isolate';
 
 final SPAWN_PACKAGE_ROOT = "file:///no/such/file/";
 
-void main([args, port]) async {
+main([args, port]) async {
   if (port != null) {
     testPackageRoot(port);
     return;
   }
   var p = new RawReceivePort();
   Isolate.spawnUri(Platform.script,
                    [],
                    p.sendPort,
                    packageRoot: Uri.parse(SPAWN_PACKAGE_ROOT));
   p.handler = (msg) {
     p.close();
     if (msg != SPAWN_PACKAGE_ROOT) {
       throw "Bad package root in child isolate: $msg";
     }
     print("SUCCESS");
   };
   print("Spawning isolate's package root: ${await Isolate.packageRoot}");
 }
 
 testPackageRoot(port) async {
   var packageRoot = await Isolate.packageRoot;
   print("Spawned isolate's package root: $packageRoot");
   port.send(packageRoot.toString());
 }