Fix cluster-fuzz regression with Workers and recursive serialization

test/mjsunit/regress/regress-crbug-503968.js

Index: test/mjsunit/regress/regress-crbug-503968.js
diff --git a/test/mjsunit/regress/regress-crbug-503968.js b/test/mjsunit/regress/regress-crbug-503968.js
new file mode 100644
index 0000000000000000000000000000000000000000..c0446da94db586271c3dcc468cb3ff289434c22d
--- /dev/null
+++ b/test/mjsunit/regress/regress-crbug-503968.js
@@ -0,0 +1,15 @@
+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+if (this.Worker) {
+  function __f_0() { this.s = new Object(); }
+  function __f_1() {
+    this.l = [new __f_0, new __f_0];
+  }
+  __v_6 = new __f_1;
+  function __f_4() {
+  }
+  var __v_9 = new Worker(__f_4);
+  __v_9.postMessage(__v_6);
+}