Implement new parameters on Isolate.spawn() for dart2js.

tests/isolate/exit_at_spawn_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.
 
 library exit_at_spawn;
 
 import "dart:isolate";
 import "dart:async";
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 
+// Isolate exiting immediately.
 isomain(args) {}
 
+// Isolate exiting after running microtasks.
+isomain2(args) {
+  scheduleMicrotask((){});
+}
+
+// Isolate exiting after running timers.
+isomain3(args) {
+  new Timer(Duration.ZERO, (){});
+}
+
 main(){
   asyncStart();
 
+  test(isomain);
+  test(isomain2);
+  test(isomain3);
+
+  asyncEnd();
+}
+
+void test(mainFunction) {
+  asyncStart();
+
   RawReceivePort exitPort = new RawReceivePort();
   exitPort.handler = (message) {
     Expect.equals(null, message);
     exitPort.close();
     asyncEnd();
   };
-  
-  Isolate.spawn(isomain,
+
+  Isolate.spawn(mainFunction,
                 null,
                 // Setup handler as part of spawn.
                 errorsAreFatal: false,
                 onExit: exitPort.sendPort);
 }