Create base::test::ScopedTaskScheduler.

base/task_scheduler/task_scheduler.h

 // 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.
 
 #ifndef BASE_TASK_SCHEDULER_TASK_SCHEDULER_H_
 #define BASE_TASK_SCHEDULER_TASK_SCHEDULER_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 64 matching lines @@
   // called once.
   virtual void Shutdown() = 0;
 
   // Waits until there are no pending undelayed tasks. May be called in tests
   // to validate that a condition is met after all undelayed tasks have run.
   //
   // Does not wait for delayed tasks. Waits for undelayed tasks posted from
   // other threads during the call. Returns immediately when shutdown completes.
   virtual void FlushForTesting() = 0;
 
+  // Joins all threads of this scheduler. Tasks that are already running are
+  // allowed to complete their execution. This can only be called once.
+  virtual void JoinForTesting() = 0;
+
   // CreateAndSetSimpleTaskScheduler(), CreateAndSetDefaultTaskScheduler(), and
   // SetInstance() register a TaskScheduler to handle tasks posted through the
   // post_task.h API for this process. The registered TaskScheduler will only be
   // deleted when a new TaskScheduler is registered and is leaked on shutdown.
   // The methods must not be called when TaskRunners created by the previous
   // TaskScheduler are still alive. The methods are not thread-safe; proper
   // synchronization is required to use the post_task.h API after registering a
   // new TaskScheduler.
 
   // Creates and sets a task scheduler with one worker pool that can have up to
@@ skipping 15 matching lines @@
 
   // Retrieve the TaskScheduler set via CreateAndSetDefaultTaskScheduler() or
   // SetInstance(). This should be used very rarely; most users of TaskScheduler
   // should use the post_task.h API.
   static TaskScheduler* GetInstance();
 };
 
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_TASK_SCHEDULER_H_