Always use an async TaskScheduler in TestBrowserThreadBundle.

chrome/browser/printing/cloud_print/test/cloud_print_proxy_process_browsertest.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.
 
 // Create a service process that uses a Mock to respond to the browser in order
 // to test launching the browser using the cloud print policy check command
 // line switch.
 
 #include <stdint.h>
 
@@ skipping 384 matching lines @@
 
    private:
     bool seen_;
     bool running_;
   };
 
   WindowedChannelConnectionObserver observer_;
 };
 
 CloudPrintProxyPolicyStartupTest::CloudPrintProxyPolicyStartupTest()
-    :  // TaskScheduler must run on its own thread because the main thread waits
-       // for a task running in it.
-      thread_bundle_(content::TestBrowserThreadBundle::REAL_IO_THREAD |
-                     content::TestBrowserThreadBundle::REAL_TASK_SCHEDULER) {
+    : thread_bundle_(content::TestBrowserThreadBundle::REAL_IO_THREAD) {
   // Although is really a unit test which runs in the browser_tests binary, it
   // doesn't get the unit setup which normally happens in the unit test binary.
   ChromeUnitTestSuite::InitializeProviders();
   ChromeUnitTestSuite::InitializeResourceBundle();
 }
 
 CloudPrintProxyPolicyStartupTest::~CloudPrintProxyPolicyStartupTest() {
 }
 
 void CloudPrintProxyPolicyStartupTest::SetUp() {
@@ skipping 123 matching lines @@
   // constructed.
   chrome::TestingIOThreadState testing_io_thread_state;
 
   base::Process process =
       Launch("CloudPrintMockService_StartEnabledWaitForQuit");
   WaitForConnect();
   ShutdownAndWaitForExitWithTimeout(std::move(process));
   ServiceProcessControl::GetInstance()->Disconnect();
   content::RunAllPendingInMessageLoop();
 }