Add base::test::ScopedTaskEnvironment.

base/test/scoped_task_environment.cc

+// Copyright 2017 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/test/scoped_task_environment.h"
+
+#include "base/run_loop.h"
+#include "base/task_scheduler/scheduler_worker_pool_params.h"
+#include "base/task_scheduler/task_scheduler.h"
+#include "base/time/time.h"
+
+namespace base {
+namespace test {
+
+ScopedTaskEnvironment::ScopedTaskEnvironment() {
+  DCHECK(!TaskScheduler::GetInstance());
+
+  // Instantiate a TaskScheduler with 1 thread in each of its 4 pools. Threads
+  // stay alive even when they don't have work.
+  constexpr int kMaxThreads = 1;
+  const TimeDelta kSuggestedReclaimTime = TimeDelta::Max();
+  const SchedulerWorkerPoolParams worker_pool_params(
+      SchedulerWorkerPoolParams::StandbyThreadPolicy::ONE, kMaxThreads,
+      kSuggestedReclaimTime);
+  TaskScheduler::CreateAndSetDefaultTaskScheduler(
+      "ScopedTaskEnvironment", {worker_pool_params, worker_pool_params,
+                                worker_pool_params, worker_pool_params});
+  task_scheduler_ = TaskScheduler::GetInstance();
+}
+
+ScopedTaskEnvironment::~ScopedTaskEnvironment() {
+  RunLoop().RunUntilIdle();
+
+  DCHECK_EQ(TaskScheduler::GetInstance(), task_scheduler_);
+  TaskScheduler::GetInstance()->Shutdown();
+  TaskScheduler::GetInstance()->JoinForTesting();
+  TaskScheduler::SetInstance(nullptr);
+}
+
+}  // namespace test
+}  // namespace base