Wrap map and set implementation in functions.

src/promise.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 $Object = global.Object
-// var $WeakMap = global.WeakMap
 
 // For bootstrapper.
 
 var IsPromise;
 var PromiseCreate;
 var PromiseResolve;
 var PromiseReject;
 var PromiseChain;
 var PromiseCatch;
 var PromiseThen;
@@ skipping 363 matching lines @@
     "race", PromiseRace,
     "resolve", PromiseCast
   ]);
   InstallFunctions($Promise.prototype, DONT_ENUM, [
     "chain", PromiseChain,
     "then", PromiseThen,
     "catch", PromiseCatch
   ]);
 
 })();