Fix ArcAppModelBuilderTest

chrome/browser/ui/app_list/app_list_test_util.cc

 // 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.
 
 #include "chrome/browser/ui/app_list/app_list_test_util.h"
 
 #include "base/files/file_path.h"
 #include "chrome/browser/extensions/extension_service.h"
 #include "chrome/common/chrome_constants.h"
 #include "extensions/browser/extension_registry.h"
@@ skipping 19 matching lines @@
   // - 2 packaged extension apps
   // - 1 hosted extension app
   base::FilePath source_install_dir =
       data_dir().AppendASCII("app_list").AppendASCII("Extensions");
   base::FilePath pref_path = source_install_dir
       .DirName()
       .Append(chrome::kPreferencesFilename);
   InitializeInstalledExtensionService(pref_path, source_install_dir);
   service_->Init();
 
+  // ExtensionService needs a real I/O thread.
+  service_->SetFileTaskRunnerForTesting(
+      content::BrowserThread::GetBlockingPool()
+          ->GetSequencedTaskRunnerWithShutdownBehavior(
+              content::BrowserThread::GetBlockingPool()->GetNamedSequenceToken(
+                  "ext_install-"),
+              base::SequencedWorkerPool::SKIP_ON_SHUTDOWN));
+
   // There should be 4 extensions in the test profile.
   ASSERT_EQ(4U, registry()->enabled_extensions().size());
 }