async/await: Don't trigger uncaught rejection handlers on throwaway Promises

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 203 matching lines @@
     "ToLowerCaseI18N",
     "ToPositiveInteger",
     "ToUpperCaseI18N",
     // From runtime:
     "is_concat_spreadable_symbol",
     "iterator_symbol",
     "promise_result_symbol",
     "promise_state_symbol",
     "promise_await_handler_symbol",
     "promise_handled_hint_symbol",
+    "promise_has_handler_symbol",
     "object_freeze",
     "object_is_frozen",
     "object_is_sealed",
     "reflect_apply",
     "reflect_construct",
     "regexp_flags_symbol",
     "to_string_tag_symbol",
     "object_to_string",
     "species_symbol",
     "match_symbol",
@@ skipping 119 matching lines @@
 
 extrasUtils.uncurryThis = function uncurryThis(func) {
   return function(thisArg, ...args) {
     return %reflect_apply(func, thisArg, args);
   };
 };
 
 %ToFastProperties(extrasUtils);
 
 })