Add TaskScheduler::JoinForTesting().

base/task_scheduler/task_scheduler_impl.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_IMPL_H_
 #define BASE_TASK_SCHEDULER_TASK_SCHEDULER_IMPL_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 26 matching lines @@
  public:
   // Creates and returns an initialized TaskSchedulerImpl. CHECKs on failure.
   // |worker_pool_params_vector| describes the worker pools to create.
   // |worker_pool_index_for_traits_callback| returns the index in |worker_pools|
   // of the worker pool in which a task with given traits should run.
   static std::unique_ptr<TaskSchedulerImpl> Create(
       const std::vector<SchedulerWorkerPoolParams>& worker_pool_params_vector,
       const WorkerPoolIndexForTraitsCallback&
           worker_pool_index_for_traits_callback);
 
-  // Destroying a TaskSchedulerImpl is not allowed in production; it is always
-  // leaked. In tests, it can only be destroyed after JoinForTesting() has
-  // returned.
   ~TaskSchedulerImpl() override;
 
   // TaskScheduler:
   void PostDelayedTaskWithTraits(const tracked_objects::Location& from_here,
                                  const TaskTraits& traits,
                                  const Closure& task,
                                  TimeDelta delay) override;
   scoped_refptr<TaskRunner> CreateTaskRunnerWithTraits(
       const TaskTraits& traits) override;
   scoped_refptr<SequencedTaskRunner> CreateSequencedTaskRunnerWithTraits(
       const TaskTraits& traits) override;
   scoped_refptr<SingleThreadTaskRunner> CreateSingleThreadTaskRunnerWithTraits(
       const TaskTraits& traits) override;
   std::vector<const HistogramBase*> GetHistograms() const override;
   void Shutdown() override;
   void FlushForTesting() override;
-
-  // Joins all threads. Tasks that are already running are allowed to complete
-  // their execution. This can only be called once.
-  void JoinForTesting();
+  void JoinForTesting() override;
 
  private:
   explicit TaskSchedulerImpl(const WorkerPoolIndexForTraitsCallback&
                                  worker_pool_index_for_traits_callback);
 
   void Initialize(
       const std::vector<SchedulerWorkerPoolParams>& worker_pool_params_vector);
 
   // Returns the worker pool that runs Tasks with |traits|.
   SchedulerWorkerPool* GetWorkerPoolForTraits(const TaskTraits& traits);
@@ skipping 13 matching lines @@
   AtomicFlag join_for_testing_returned_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(TaskSchedulerImpl);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_TASK_SCHEDULER_IMPL_H_