diff -r 000000000000 -r 6474c204b198 addon-sdk/source/lib/sdk/util/iteration.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/addon-sdk/source/lib/sdk/util/iteration.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,33 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+'use strict';
+
+module.metadata = {
+  "stability": "experimental"
+};
+
+// This is known as @@iterator in the ES6 spec.  Until it is bound to
+// some well-known name, find the @@iterator object by expecting it as
+// the first property accessed on a for-of iterable.
+const iteratorSymbol = (function() {
+  try {
+    for (var _ of Proxy.create({get: function(_, name) { throw name; } }))
+      break;
+  } catch (name) {
+    return name;
+  }
+  throw new TypeError;
+})();
+
+exports.iteratorSymbol = iteratorSymbol;
+
+// An adaptor that, given an object that is iterable with for-of, is
+// suitable for being bound to __iterator__ in order to make the object
+// iterable in the same way via for-in.
+function forInIterator() {
+    for (let item of this)
+        yield item;
+}
+
+exports.forInIterator = forInIterator;