[promises] don't store undefined resulting from ResolvePromise

src/js/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.
 
 (function(global, utils, extrasUtils) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
@@ skipping 471 matching lines @@
 // Promise.resolve ( x )
 function PromiseResolve(x) {
   if (!IS_RECEIVER(this)) {
     throw %make_type_error(kCalledOnNonObject, PromiseResolve);
   }
   if (IsPromise(x) && x.constructor === this) return x;
 
   // Avoid creating resolving functions.
   if (this === GlobalPromise) {
     var promise = PromiseCreate();
-    var resolveResult = ResolvePromise(promise, x);
+    ResolvePromise(promise, x);
     return promise;
   }
 
   // debugEvent is not so meaningful here as it will be resolved
   var promiseCapability = NewPromiseCapability(this, true);
-  var resolveResult = %_Call(promiseCapability.resolve, UNDEFINED, x);
+  %_Call(promiseCapability.resolve, UNDEFINED, x);
   return promiseCapability.promise;
 }
 
 // ES#sec-promise.all
 // Promise.all ( iterable )
 function PromiseAll(iterable) {
   if (!IS_RECEIVER(this)) {
     throw %make_type_error(kCalledOnNonObject, "Promise.all");
   }
 
@@ skipping 200 matching lines @@
   to.PromiseNextMicrotaskID = PromiseNextMicrotaskID;
 
   to.GlobalPromise = GlobalPromise;
   to.NewPromiseCapability = NewPromiseCapability;
   to.PerformPromiseThen = PerformPromiseThen;
   to.ResolvePromise = ResolvePromise;
   to.RejectPromise = RejectPromise;
 });
 
 })