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diff --git a/dom/browser-element/mochitest/async.js b/dom/browser-element/mochitest/async.js
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+/* 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/. */
+
+/*
+ * This is an approximate implementation of ES7's async-await pattern.
+ * see: https://github.com/tc39/ecmascript-asyncawait
+ *
+ * It allows for simple creation of async function and "tasks".
+ *
+ * For example:
+ *
+ *  var myThinger = {
+ *    doAsynThing: async(function*(url){
+ *      var result = yield fetch(url);
+ *      return process(result);
+ *    });
+ * }
+ *
+ * And Task-like things can be created as follows:
+ *
+ * var myTask = async(function*{
+ *   var result = yield fetch(url);
+ *   return result;
+ * });
+ * //returns a promise
+ *
+ * myTask().then(doSomethingElse);
+ *
+ */
+
+(function(exports) {
+  "use strict";
+  function async(func, self) {
+    return function asyncFunction() {
+      const functionArgs = Array.from(arguments);
+      return new Promise(function(resolve, reject) {
+        var gen;
+        if (typeof func !== "function") {
+          reject(new TypeError("Expected a Function."));
+        }
+        //not a generator, wrap it.
+        if (func.constructor.name !== "GeneratorFunction") {
+          gen = (function*() {
+            return func.apply(self, functionArgs);
+          }());
+        } else {
+          gen = func.apply(self, functionArgs);
+        }
+        try {
+          step(gen.next(undefined));
+        } catch (err) {
+          reject(err);
+        }
+
+        function step({value, done}) {
+          if (done) {
+            return resolve(value);
+          }
+          if (value instanceof Promise) {
+            return value.then(
+              result => step(gen.next(result)),
+              error => {
+                try {
+                  step(gen.throw(error));
+                } catch (err) {
+                  throw err;
+                }
+              }
+            ).catch(err => reject(err));
+          }
+          step(gen.next(value));
+        }
+      });
+    };
+  }
+  exports.async = async;
+}(this || self));