Fix for issue 21398 (only send "literal like" objects across isolates spawned using spawnURI

tests/isolate/issue_21398_parent_isolate_test.dart

Index: tests/isolate/issue_21398_parent_isolate_test.dart
===================================================================
--- tests/isolate/issue_21398_parent_isolate_test.dart	(revision 0)
+++ tests/isolate/issue_21398_parent_isolate_test.dart	(working copy)
@@ -0,0 +1,65 @@
+// 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:isolate';
+import 'dart:async';
+import "package:expect/expect.dart";
+
+class FromMainIsolate {
+  String toString() => 'from main isolate';
+  int get fld => 10;
+}
+
+funcChild(args) {
+  var reply = args[1];
+  var obj = args[0];
+  Expect.isTrue(obj is FromMainIsolate);
+  Expect.equals(10, obj.fld);
+  reply.send(new FromMainIsolate());
+}
+
+main() {
+  var receive1 = new ReceivePort();
+  var receive2 = new ReceivePort();
+
+  // First spawn an isolate using spawnURI and have it
+  // send back a "non-literal" like object.
+  Isolate.spawnUri(Uri.parse('issue_21398_child_isolate.dart'),
+                   [],
+                   [new FromMainIsolate(), receive1.sendPort]).catchError(
+    (error) {
+      Expect.isTrue(error is ArgumentError);
+    }
+  );
+  Isolate.spawnUri(Uri.parse('issue_21398_child_isolate.dart'),
+                   [],
+                   receive1.sendPort).then(
+    (isolate) {
+      receive1.listen(
+        (msg) {
+          Expect.stringEquals(msg, "Invalid Argument(s).");
+          receive1.close();
+        },
+        onError: (e) => print('$e')
+      );
+    }
+  );
+
+  // Now spawn an isolate using spawnFunction and send it a "non-literal"
+  // like object and also have the child isolate send back a "non-literal"
+  // like object.
+  Isolate.spawn(funcChild, 
+                [new FromMainIsolate(), receive2.sendPort]).then(
+    (isolate) {
+      receive2.listen(
+        (msg) {
+          Expect.isTrue(msg is FromMainIsolate);
+          Expect.equals(10, msg.fld);
+          receive2.close();
+        },
+        onError: (e) => print('$e')
+      );
+    }
+  );
+}