Implement well-known symbol `Symbol.toStringTag`

src/collection.js

 // Copyright 2012 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.
 
 "use strict";
 
 // This file relies on the fact that the following declaration has been made
 // in runtime.js:
 // var $Array = global.Array;
 
@@ skipping 130 matching lines @@
 
 
 // -------------------------------------------------------------------
 
 function SetUpSet() {
   %CheckIsBootstrapping();
 
   %SetCode($Set, SetConstructor);
   %FunctionSetPrototype($Set, new $Object());
   %AddNamedProperty($Set.prototype, "constructor", $Set, DONT_ENUM);
+  %AddNamedProperty($Set.prototype, symbolToStringTag, "Set",  DONT_ENUM | READ_ONLY);
 
   %FunctionSetLength(SetForEach, 1);
 
   // Set up the non-enumerable functions on the Set prototype object.
   InstallGetter($Set.prototype, "size", SetGetSizeJS);
   InstallFunctions($Set.prototype, DONT_ENUM, $Array(
     "add", SetAddJS,
     "has", SetHasJS,
     "delete", SetDeleteJS,
     "clear", SetClearJS,
@@ skipping 115 matching lines @@
 
 
 // -------------------------------------------------------------------
 
 function SetUpMap() {
   %CheckIsBootstrapping();
 
   %SetCode($Map, MapConstructor);
   %FunctionSetPrototype($Map, new $Object());
   %AddNamedProperty($Map.prototype, "constructor", $Map, DONT_ENUM);
+  %AddNamedProperty($Map.prototype, symbolToStringTag, "Map",  DONT_ENUM | READ_ONLY);
 
   %FunctionSetLength(MapForEach, 1);
 
   // Set up the non-enumerable functions on the Map prototype object.
   InstallGetter($Map.prototype, "size", MapGetSizeJS);
   InstallFunctions($Map.prototype, DONT_ENUM, $Array(
     "get", MapGetJS,
     "set", MapSetJS,
     "has", MapHasJS,
     "delete", MapDeleteJS,
     "clear", MapClearJS,
     "forEach", MapForEach
   ));
 }
 
 SetUpMap();