Allow ScopedTaskEnvironment to pump UI or IO messages on the main thread.

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() {
+ScopedTaskEnvironment::ScopedTaskEnvironment(MainThreadType main_thread_type)
+    : message_loop_(main_thread_type == MainThreadType::UI
+                        ? MessageLoop::TYPE_UI
+                        : MessageLoop::TYPE_IO) {
   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_);
   // Without FlushForTesting(), DeleteSoon() and ReleaseSoon() tasks could be
   // skipped, resulting in memory leaks.
   TaskScheduler::GetInstance()->FlushForTesting();
   TaskScheduler::GetInstance()->Shutdown();
   TaskScheduler::GetInstance()->JoinForTesting();
   TaskScheduler::SetInstance(nullptr);
 }
 
 }  // namespace test
 }  // namespace base