Revert of Disallow posting tasks to SequencedWorkerPools by default.

base/threading/sequenced_worker_pool_unittest.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/threading/sequenced_worker_pool.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <memory>
@@ skipping 235 matching lines @@
   void SetUp() override {
     if (RedirectedToTaskScheduler()) {
       std::vector<SchedulerWorkerPoolParams> worker_pool_params;
       worker_pool_params.emplace_back(
           "SchedulerWorkerPoolName", ThreadPriority::NORMAL,
           SchedulerWorkerPoolParams::IORestriction::ALLOWED, kNumWorkerThreads,
           TimeDelta::Max());
       TaskScheduler::CreateAndSetDefaultTaskScheduler(
           std::move(worker_pool_params),
           base::Bind([](const TaskTraits&) -> size_t { return 0U; }));
-
-      // Unit tests run in an environment where SequencedWorkerPool is enabled
-      // without redirection to TaskScheduler. For the current unit test,
-      // disable it and re-enable it with redirection to TaskScheduler.
-      SequencedWorkerPool::DisableForProcessForTesting();
-      SequencedWorkerPool::EnableWithRedirectionToTaskSchedulerForProcess();
+      SequencedWorkerPool::ResetRedirectToTaskSchedulerForProcessForTesting();
+      SequencedWorkerPool::RedirectToTaskSchedulerForProcess();
     }
   }
 
   void TearDown() override {
     // Wait until all references to the SequencedWorkerPool are gone and destroy
     // it. This must be done before destroying the TaskScheduler. Otherwise, the
     // SequencedWorkerPool could try to redirect tasks to a destroyed
     // TaskScheduler.
     DeletePool();
 
     if (RedirectedToTaskScheduler()) {
-      // Reset SequencedWorkerPool to its original state (i.e. enabled without
-      // redirection to TaskScheduler).
-      SequencedWorkerPool::DisableForProcessForTesting();
-      SequencedWorkerPool::EnableForProcess();
-
-      // Delete the registered TaskScheduler.
+      SequencedWorkerPool::ResetRedirectToTaskSchedulerForProcessForTesting();
       DeleteTaskScheduler();
     }
   }
 
   bool RedirectedToTaskScheduler() const {
     return GetParam() == SequencedWorkerPoolRedirection::TO_TASK_SCHEDULER;
   }
 
   const scoped_refptr<SequencedWorkerPool>& pool() {
     return pool_owner_->pool();
@@ skipping 951 matching lines @@
     SequencedWorkerPoolSequencedTaskRunner, SequencedTaskRunnerTest,
     SequencedWorkerPoolSequencedTaskRunnerTestDelegate);
 INSTANTIATE_TYPED_TEST_CASE_P(
     SequencedWorkerPoolSequencedTaskRunner,
     SequencedTaskRunnerDelayedTest,
     SequencedWorkerPoolSequencedTaskRunnerTestDelegate);
 
 }  // namespace
 
 }  // namespace base