[intl] Avoid modifying options bag from constructor

test/intl/date-format/unmodified-options.js

Index: test/intl/date-format/unmodified-options.js
diff --git a/test/intl/date-format/unmodified-options.js b/test/intl/date-format/unmodified-options.js
new file mode 100644
index 0000000000000000000000000000000000000000..4a013660a8cb325055aeeb716079ebab6bfa55ba
--- /dev/null
+++ b/test/intl/date-format/unmodified-options.js
@@ -0,0 +1,17 @@
+// Copyright 2016 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.
+
+let options = {};
+new Intl.DateTimeFormat(undefined, options);
+assertEquals([], Object.getOwnPropertyNames(options));
+
+let date = new Date();
+date.toLocaleString(undefined, options);
+assertEquals([], Object.getOwnPropertyNames(options));
+
+date.toLocaleDateString(undefined, options);
+assertEquals([], Object.getOwnPropertyNames(options));
+
+date.toLocaleTimeString(undefined, options);
+assertEquals([], Object.getOwnPropertyNames(options));