Add pollyfills to the error-overlay iframe script

packages/react-error-overlay/package.json

@@ -36,6 +36,8 @@
     "babel-loader": "^7.1.2",
     "babel-runtime": "6.26.0",
     "html-entities": "1.2.1",
+    "object-assign": "^4.1.1",
+    "promise": "^8.0.1",
     "react": "^15 || ^16",
     "react-dom": "^15 || ^16",
     "settle-promise": "1.0.0",

packages/react-error-overlay/src/iframeScript.js

@@ -6,6 +6,7 @@
  * 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.
  */
+import './utils/pollyfills.js';
 import React from 'react';
 import ReactDOM from 'react-dom';
 import CompileErrorContainer from './containers/CompileErrorContainer';

packages/react-error-overlay/src/utils/pollyfills.js

@@ -0,0 +1,21 @@
+/**
+ * Copyright (c) 2015-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.
+ */
+'use strict';
+
+if (typeof Promise === 'undefined') {
+  // Rejection tracking prevents a common issue where React gets into an
+  // inconsistent state due to an error, but it gets swallowed by a Promise,
+  // and the user has no idea what causes React's erratic future behavior.
+  require('promise/lib/rejection-tracking').enable();
+  window.Promise = require('promise/lib/es6-extensions.js');
+}
+
+// Object.assign() is commonly used with React.
+// It will use the native implementation if it's present and isn't buggy.
+Object.assign = require('object-assign');