Add a gulp script for extracting error codes (#6882)

(cherry picked from commit bfd1531eca)

scripts/error-codes/invertObject.js

@@ -0,0 +1,35 @@
+/**
+ * Copyright (c) 2013-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
+ */
+'use strict';
+
+/*:: import type { ErrorMap } from './Types' */
+
+/**
+ * turns
+ *   { 'MUCH ERROR': '0', 'SUCH WRONG': '1' }
+ * into
+ *   { 0: 'MUCH ERROR', 1: 'SUCH WRONG' }
+ */
+function invertObject(targetObj/* : ErrorMap */)/* : ErrorMap */ {
+  var result = {};
+  var mapKeys = Object.keys(targetObj);
+
+  for (let i = 0; i < mapKeys.length; i++) {
+    var originalKey = mapKeys[i];
+    var originalVal = targetObj[originalKey];
+
+    result[originalVal] = originalKey;
+  }
+
+  return result;
+}
+
+module.exports = invertObject;