Enables clean VM shutdown.

runtime/tests/vm/dart/spawn_shutdown_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:async';
+import 'dart:isolate';
+
+// Spawn an isolate |foo| that will continue trying to spawn isolates even after
+// the timer in |main| completes. This test ensures that the VM can shutdown
+// correctly even while an isolate is attempting to spawn more isolates.
+
+isolate1(sendPort) {
+  var receivePort = new ReceivePort();
+  sendPort.send(receivePort.sendPort);
+  receivePort.listen((msg) {});
+}
+
+void foo(int count) {
+  for (int i = 0; i < count; i++) {
+    var receivePort = new ReceivePort();
+    Isolate.spawn(isolate1, receivePort.sendPort);
+    receivePort.listen((sendPort) {
+      Isolate.spawn(isolate1,sendPort);
+      receivePort.close();
+    });
+  }
+}
+
+void main() {
+  Isolate.spawn(foo, 100);
+  new Timer(const Duration(seconds: 10), () {});
+}