Implement the `RegExp.prototype.flags` getter

src/bootstrapper.cc

 // Copyright 2014 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.
 
 #include "src/bootstrapper.h"
 
 #include "src/accessors.h"
 #include "src/code-stubs.h"
 #include "src/extensions/externalize-string-extension.h"
 #include "src/extensions/free-buffer-extension.h"
@@ skipping 2148 matching lines @@
   static const char* harmony_array_includes_natives[] = {
       "native harmony-array-includes.js", NULL};
   static const char* harmony_proxies_natives[] = {"native proxy.js", NULL};
   static const char* harmony_strings_natives[] = {"native harmony-string.js",
                                                   NULL};
   static const char* harmony_classes_natives[] = {"native harmony-classes.js",
                                                   NULL};
   static const char* harmony_modules_natives[] = {NULL};
   static const char* harmony_scoping_natives[] = {NULL};
   static const char* harmony_object_literals_natives[] = {NULL};
-  static const char* harmony_regexps_natives[] = {NULL};
+  static const char* harmony_regexps_natives[] = {
+      "native harmony-regexp.js", NULL};
   static const char* harmony_arrow_functions_natives[] = {NULL};
   static const char* harmony_numeric_literals_natives[] = {NULL};
   static const char* harmony_tostring_natives[] = {"native harmony-tostring.js",
                                                    NULL};
   static const char* harmony_templates_natives[] = {
       "native harmony-templates.js", NULL};
   static const char* harmony_sloppy_natives[] = {NULL};
   static const char* harmony_unicode_natives[] = {NULL};
 
   for (int i = ExperimentalNatives::GetDebuggerCount();
@@ skipping 643 matching lines @@
   return from + sizeof(NestingCounterType);
 }
 
 
 // Called when the top-level V8 mutex is destroyed.
 void Bootstrapper::FreeThreadResources() {
   DCHECK(!IsActive());
 }
 
 } }  // namespace v8::internal