Remove unnecessary coupling between Promise tests and Object.observe

test/promises-aplus/lib/mocha.js

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 24 matching lines @@
 var beforeEach;
 var afterEach;
 var RunAllTests;
 
 var assert = require('assert');
 
 (function() {
 var TIMEOUT = 1000;
 
 function PostMicrotask(fn) {
-  var o = {};
-  Object.observe(o, function() {
-    fn();
-  });
-  // Change something to enqueue a microtask.
-  o.x = 'hello';
+  Promise.resolve().then(fn);
 }
 
 var context = {
   beingDescribed: undefined,
   currentSuiteIndex: 0,
   suites: []
 };
 
 function Run() {
   function current() {
@@ skipping 194 matching lines @@
 
 beforeEach = function(fn) {
   context.beingDescribed.beforeEach = fn;
 }
 
 afterEach = function(fn) {
   context.beingDescribed.afterEach = fn;
 }
 
 }());