Revert of Disabled flaky test AppBackgroundPageApiTest.NoJsBackgroundPage

chrome/browser/extensions/app_background_page_apitest.cc

 // Copyright (c) 2012 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.
 
 #include "base/location.h"
 #include "base/path_service.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/threading/thread_task_runner_handle.h"
@@ skipping 286 matching lines @@
   // the app was loaded.
   ASSERT_TRUE(WaitForBackgroundMode(true));
 
   const Extension* extension = GetSingleLoadedExtension();
   ASSERT_TRUE(
       BackgroundContentsServiceFactory::GetForProfile(browser()->profile())->
           GetAppBackgroundContents(ASCIIToUTF16(extension->id())));
   UnloadExtension(extension->id());
 }
 
-// TODO(crbug.com/642482) Disabled test for flakyness.
-IN_PROC_BROWSER_TEST_F(AppBackgroundPageApiTest, DISABLED_NoJsBackgroundPage) {
+IN_PROC_BROWSER_TEST_F(AppBackgroundPageApiTest, NoJsBackgroundPage) {
   // Keep the task manager up through this test to verify that a crash doesn't
   // happen when window.open creates a background page that switches
   // RenderViewHosts. See http://crbug.com/165138.
   chrome::ShowTaskManager(browser());
 
   // Make sure that no BackgroundContentses get deleted (a signal that repeated
   // window.open calls recreate instances, instead of being no-ops).
   content::TestNotificationTracker background_deleted_tracker;
   background_deleted_tracker.ListenFor(
       chrome::NOTIFICATION_BACKGROUND_CONTENTS_DELETED,
@@ skipping 316 matching lines @@
       extensions::ProcessManager::Get(browser()->profile());
   ImpulseCallbackCounter idle_impulse_counter(manager, extension()->id());
   EXPECT_TRUE(nacl_modules_loaded.WaitUntilSatisfied());
 
   manager->SetKeepaliveImpulseDecrementCallbackForTesting(
       idle_impulse_counter.SetGoalAndGetCallback(1));
   nacl_modules_loaded.Reply("be idle");
   idle_impulse_counter.Wait();
 #endif
 }