Fix a leak in extensions_unittests.

extensions/test/data/unit_test_environment_specific_bindings.js

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-var nativesPromise = requireAsync('testNatives');
 var sendRequestNatives = requireNative('sendRequest');
 
 function registerHooks(api) {
   var chromeTest = api.compiledApi;
   var apiFunctions = api.apiFunctions;
 
   apiFunctions.setHandleRequest('notifyPass', function() {
-    nativesPromise.then(function(natives) {
+    requireAsync('testNatives').then(function(natives) {
       natives.NotifyPass();
     });
   });
 
   apiFunctions.setHandleRequest('notifyFail', function(message) {
-    nativesPromise.then(function(natives) {
+    requireAsync('testNatives').then(function(natives) {
       natives.NotifyFail(message);
     });
   });
 
   apiFunctions.setHandleRequest('log', function() {
-    nativesPromise.then(function(natives) {
+    requireAsync('testNatives').then(function(natives) {
       natives.Log($Array.join(arguments, ' '));
     });
   });
 
 }
 
 function testDone(runNextTest) {
     // Use a promise here to allow previous test contexts to be eligible for
     // garbage collection.
     Promise.resolve().then(function() {
@@ skipping 102 matching lines @@
  */
 TimeoutManager.prototype.clearTimeout_ = function(timeoutId) {
   if (this.timeouts_[timeoutId])
     delete this.timeouts_[timeoutId];
 };
 
 exports.registerHooks = registerHooks;
 exports.testDone = testDone;
 exports.exportTests = exportTests;
 exports.TimeoutManager = TimeoutManager;