Add base::test::ScopedAsyncTaskScheduler.

base/test/scoped_async_task_scheduler.cc

Index: base/test/scoped_async_task_scheduler.cc
diff --git a/base/test/scoped_async_task_scheduler.cc b/base/test/scoped_async_task_scheduler.cc
new file mode 100644
index 0000000000000000000000000000000000000000..824b07fba930680f9a019f4a10fc044a1269ba55
--- /dev/null
+++ b/base/test/scoped_async_task_scheduler.cc
@@ -0,0 +1,39 @@
+// 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_async_task_scheduler.h"
+
+#include <vector>
+
+#include "base/bind.h"
+#include "base/logging.h"
+#include "base/task_scheduler/scheduler_worker_pool_params.h"
+#include "base/task_scheduler/task_scheduler.h"
+
+namespace base {
+namespace test {
+
+ScopedAsyncTaskScheduler::ScopedAsyncTaskScheduler() {
+  DCHECK(!TaskScheduler::GetInstance());
+  constexpr int kMaxThreads = 1;
+  const TimeDelta kSuggestedReclaimTime = TimeDelta::Max();
+  std::vector<SchedulerWorkerPoolParams> worker_pool_params_vector;
+  worker_pool_params_vector.emplace_back(
+      "ScopedAsyncTaskScheduler", ThreadPriority::NORMAL,
+      SchedulerWorkerPoolParams::StandbyThreadPolicy::LAZY, kMaxThreads,
+      kSuggestedReclaimTime);
+  TaskScheduler::CreateAndSetDefaultTaskScheduler(
+      worker_pool_params_vector,
+      Bind([](const TaskTraits&) -> size_t { return 0; }));
+  task_scheduler_ = TaskScheduler::GetInstance();
+}
+
+ScopedAsyncTaskScheduler::~ScopedAsyncTaskScheduler() {
+  DCHECK_EQ(TaskScheduler::GetInstance(), task_scheduler_);
+  TaskScheduler::GetInstance()->Shutdown();
+  TaskScheduler::SetInstance(nullptr);
+}
+
+}  // namespace test
+}  // namespace base