Implement AP2 Promises

LayoutTests/fast/js/resources/Promise-resolve-in-workers.js

 importScripts('./js-test-pre.js');
 
 description('Test Promise.');
 
 var global = this;
 global.jsTestIsAsync = true;
 
 var firstPromise = new Promise(function(resolve) {
   resolve('hello');
 });
 
 var secondPromise = firstPromise.then(function(result) {
   global.thisInFulfillCallback = this;
-  shouldBeTrue('thisInFulfillCallback === secondPromise');
+  shouldBeFalse('thisInFulfillCallback === secondPromise');
+  shouldBeTrue('thisInFulfillCallback === global');
   global.result = result;
   shouldBeEqualToString('result', 'hello');
   finishJSTest();
 }, function() {
   fail('rejected');
   finishJSTest();
 });