[es6] Fix length property of collection constructors

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 218 matching lines @@
   while (%SetIteratorNext(iterator, value_array)) {
     if (stepping) %DebugPrepareStepInIfStepping(f);
     key = value_array[0];
     var new_receiver = needs_wrapper ? ToObject(receiver) : receiver;
     %_CallFunction(new_receiver, key, key, this, f);
   }
 }
 
 
 %SetCode($Set, SetConstructor);
+%FunctionSetLength($Set, 0);
 %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($Set.prototype, "size", SetGetSize);
 InstallFunctions($Set.prototype, DONT_ENUM, $Array(
@@ skipping 168 matching lines @@
   var value_array = [UNDEFINED, UNDEFINED];
   while (%MapIteratorNext(iterator, value_array)) {
     if (stepping) %DebugPrepareStepInIfStepping(f);
     var new_receiver = needs_wrapper ? ToObject(receiver) : receiver;
     %_CallFunction(new_receiver, value_array[1], value_array[0], this, f);
   }
 }
 
 
 %SetCode($Map, MapConstructor);
+%FunctionSetLength($Map, 0);
 %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($Map.prototype, "size", MapGetSize);
 InstallFunctions($Map.prototype, DONT_ENUM, $Array(
   "get", MapGet,
   "set", MapSet,
   "has", MapHas,
   "delete", MapDelete,
   "clear", MapClearJS,
   "forEach", MapForEach
 ));
 
 })();