Create base::test::ScopedTaskScheduler.

base/test/scoped_task_scheduler.cc

+// Copyright 2016 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_scheduler.h"
+
+#include "base/task_scheduler/task_scheduler.h"
+#include "base/time/time.h"
+
+namespace base {
+namespace test {
+
+ScopedTaskScheduler::ScopedTaskScheduler() {
+  DCHECK(!TaskScheduler::GetInstance());
+
+  // Create a TaskScheduler with a single thread to make tests deterministic.
+  constexpr int kMaxThreads = 1;
+  const TimeDelta kDetachDuration = base::TimeDelta::Max();

[gab, 2016/11/17 14:39:35]

FYI, TimeDelta can be constexpr too (but by comment on other CL I suspect we
don't need this param).

+  TaskScheduler::CreateAndSetSimpleTaskScheduler(kMaxThreads, kDetachDuration);
+  task_scheduler_ = TaskScheduler::GetInstance();
+}
+
+ScopedTaskScheduler::~ScopedTaskScheduler() {
+  DCHECK_EQ(task_scheduler_, TaskScheduler::GetInstance());
+  TaskScheduler::GetInstance()->Shutdown();
+  TaskScheduler::GetInstance()->JoinForTesting();
+  TaskScheduler::SetInstance(nullptr);
+}
+
+}  // namespace test
+}  // namespace base