An isolate created with spawn function doesn't necessarily agree with its parent on the library pri…

tests/isolate/send_private_test.dart

+// Copyright (c) 2016, 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:isolate";
+import "package:expect/expect.dart";
+
+class _Private {
+  String data;
+  _Private(this.data);
+}
+
+void child(message) {
+  print("Got message: $message");
+  SendPort replyPort = message[0];
+  _Private object = message[1];
+  Expect.isTrue(object is _Private);
+  Expect.equals("XYZ", object.data);
+  replyPort.send(object);
+}
+
+void main() {
+  var port;
+  port = new RawReceivePort((message) {
+    print("Got reply: $message");
+    Expect.isTrue(message is _Private);
+    Expect.equals("XYZ", message.data);
+    port.close();
+  });
+
+  Isolate.spawn(child, [port.sendPort, new _Private("XYZ")]);
+}