Do not flush SequencedWorkerPools in browser tests.

ios/web/test/web_test_suite.mm

 // Copyright 2013 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 "ios/web/public/test/web_test_suite.h"
 
-#include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/metrics/statistics_recorder.h"
 #include "base/path_service.h"
 #import "ios/web/public/test/test_web_client.h"
 #include "ios/web/public/url_schemes.h"
-#include "ios/web/web_thread_impl.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/base/resource/resource_bundle.h"
 
 namespace web {
 
-class WebTestSuiteListener : public testing::EmptyTestEventListener {
- public:
-  WebTestSuiteListener() {}
-  void OnTestEnd(const testing::TestInfo& test_info) override {
-    WebThreadImpl::FlushThreadPoolHelperForTesting();
-  }
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(WebTestSuiteListener);
-};
-
 WebTestSuite::WebTestSuite(int argc, char** argv)
     : base::TestSuite(argc, argv),
       web_client_(base::WrapUnique(new TestWebClient)) {}
 
 WebTestSuite::~WebTestSuite() {}
 
 void WebTestSuite::Initialize() {
   base::TestSuite::Initialize();
 
   // Initialize the histograms subsystem, so that any histograms hit in tests
   // are correctly registered with the statistics recorder and can be queried
   // by tests.
   base::StatisticsRecorder::Initialize();
 
-  testing::UnitTest::GetInstance()->listeners().Append(
-      new WebTestSuiteListener);
-
   RegisterWebSchemes(false);
 
   // Force unittests to run using en-US so if testing string output will work
   // regardless of the system language.
   ui::ResourceBundle::InitSharedInstanceWithLocale(
       "en-US", nullptr, ui::ResourceBundle::LOAD_COMMON_RESOURCES);
   base::FilePath resources_pack_path;
   base::PathService::Get(base::DIR_MODULE, &resources_pack_path);
   resources_pack_path =
       resources_pack_path.Append(FILE_PATH_LITERAL("resources.pak"));
   ResourceBundle::GetSharedInstance().AddDataPackFromPath(
       resources_pack_path, ui::SCALE_FACTOR_NONE);
 }
 
 void WebTestSuite::Shutdown() {
   ResourceBundle::CleanupSharedInstance();
   base::TestSuite::Shutdown();
 }
 
 }  // namespace web