Implement flag and source getters on RegExp.prototype.

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 199 matching lines @@
     "SymbolToString",
     "ToNameArray",
     "ToPositiveInteger",
     // From runtime:
     "is_concat_spreadable_symbol",
     "iterator_symbol",
     "promise_status_symbol",
     "promise_value_symbol",
     "reflect_apply",
     "reflect_construct",
+    "regexp_flags_symbol",
     "to_string_tag_symbol",
   ];
 
   var filtered_exports = {};
   %OptimizeObjectForAddingMultipleProperties(
       filtered_exports, expose_list.length);
   for (var key of expose_list) {
     filtered_exports[key] = exports_container[key];
   }
   %ToFastProperties(filtered_exports);
@@ skipping 116 matching lines @@
 
 extrasUtils.uncurryThis = function uncurryThis(func) {
   return function(thisArg) {
     return %Apply(func, thisArg, arguments, 1, arguments.length - 1);
   };
 };
 
 %ToFastProperties(extrasUtils);
 
 })