Fix Promise.resolve/Promise.reject unnecessarily scheduling a microtask.

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
@@ skipping 56 matching lines @@
     return promise;
   }
 
   function PromiseInit(promise) {
     return PromiseSet(
         promise, 0, UNDEFINED, new InternalArray, new InternalArray)
   }
 
   function PromiseDone(promise, status, value, promiseQueue) {
     if (GET_PRIVATE(promise, promiseStatus) === 0) {
-      PromiseEnqueue(value, GET_PRIVATE(promise, promiseQueue), status);
+      var tasks = GET_PRIVATE(promise, promiseQueue);
+      if (tasks.length) PromiseEnqueue(value, tasks, status);
       PromiseSet(promise, status, value);
     }
   }
 
   function PromiseCoerce(constructor, x) {
     if (!IsPromise(x) && IS_SPEC_OBJECT(x)) {
       var then;
       try {
         then = x.then;
       } catch(r) {
@@ skipping 295 matching lines @@
     "race", PromiseOne,
     "resolve", PromiseCast
   ]);
   InstallFunctions($Promise.prototype, DONT_ENUM, [
     "chain", PromiseChain,
     "then", PromiseThen,
     "catch", PromiseCatch
   ]);
 
 })();