Desugar async/await to create the resulting Promise upfront

src/js/prologue.js

 // Copyright 2015 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.
 
 (function(global, utils, extrasUtils) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
@@ skipping 189 matching lines @@
     "NumberIsInteger",
     "PerformPromiseThen",
     "PromiseCastResolved",
     "PromiseThen",
     "RegExpSubclassExecJS",
     "RegExpSubclassMatch",
     "RegExpSubclassReplace",
     "RegExpSubclassSearch",
     "RegExpSubclassSplit",
     "RegExpSubclassTest",
+    "RejectPromise",
     "SetIterator",
     "SetIteratorNext",
     "SetValues",
     "ToLocaleLowerCaseI18N",
     "ToLocaleUpperCaseI18N",
     "ToLowerCaseI18N",
     "ToPositiveInteger",
     "ToUpperCaseI18N",
     // From runtime:
     "is_concat_spreadable_symbol",
@@ skipping 132 matching lines @@
 
 extrasUtils.uncurryThis = function uncurryThis(func) {
   return function(thisArg, ...args) {
     return %reflect_apply(func, thisArg, args);
   };
 };
 
 %ToFastProperties(extrasUtils);
 
 })