Fix |RunMicrotasks()| leaking reference to the last context being run on.

src/promise.js

 // Copyright 2012 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 155 matching lines @@
       break;
   }
   return deferred.promise;
 }
 
 function PromiseCatch(onReject) {
   return this.then(UNDEFINED, onReject);
 }
 
 function PromiseEnqueue(value, tasks) {
-  GetMicrotaskQueue().push(function() {
+  EnqueueMicrotask(function() {
     for (var i = 0; i < tasks.length; i += 2) {
       PromiseHandle(value, tasks[i], tasks[i + 1])
     }
   });
-
-  %SetMicrotaskPending(true);
 }
 
 function PromiseHandle(value, handler, deferred) {
   try {
     var result = handler(value);
     if (result === deferred.promise)
       throw MakeTypeError('promise_cyclic', [result]);
     else if (IsPromise(result))
       %_CallFunction(result, deferred.resolve, deferred.reject, PromiseChain);
     else
@@ skipping 125 matching lines @@
     "resolve", PromiseCast
   ]);
   InstallFunctions($Promise.prototype, DONT_ENUM, [
     "chain", PromiseChain,
     "then", PromiseThen,
     "catch", PromiseCatch
   ]);
 }
 
 SetUpPromise();