Ensures that stubs added to each object pool on x64

tests/standalone/io/directory_list_sync_test.dart

Index: tests/standalone/io/directory_list_sync_test.dart
===================================================================
--- tests/standalone/io/directory_list_sync_test.dart	(revision 0)
+++ tests/standalone/io/directory_list_sync_test.dart	(revision 0)
@@ -0,0 +1,14 @@
+// Copyright (c) 2014, 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';
+
+void main() {
+  File script = new File.fromUri(Platform.script);
+  // tests/standalone/io/../../..
+  Directory startingDir = script.parent.parent.parent.parent;
+  List<FileSystemEntity> each =
+      startingDir.listSync(recursive: true, followLinks: false);
+  print("Found: ${each.length} entities");
+}