Add base::test::ScopedTaskEnvironment.

base/test/scoped_async_task_scheduler.h

 // 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.
 
 #ifndef BASE_TEST_SCOPED_ASYNC_TASK_SCHEDULER_H_
 #define BASE_TEST_SCOPED_ASYNC_TASK_SCHEDULER_H_
 
 #include "base/macros.h"
 
 namespace base {
 
 class TaskScheduler;
 
 namespace test {
 
 // Allows usage of the base/task_scheduler/post_task.h API within its scope.
 //
 // To wait until all tasks posted without a delay have run, use
 // TaskScheduler::GetInstance()->FlushForTesting().
+//
+// Deprecated. Use ScopedTaskEnvironment instead. https://crbug.com/708584
+//
+// TODO(fdoray): Replace ScopedAsyncTaskScheduler instances by
+// ScopedTaskEnvironment.
 class ScopedAsyncTaskScheduler {
  public:
   // Registers a single-threaded TaskScheduler.
   ScopedAsyncTaskScheduler();
 
   // Shuts down and unregisters the TaskScheduler.
   //
   // It is guaranteed that all BLOCK_SHUTDOWN tasks have run when this returns.
   ~ScopedAsyncTaskScheduler();
 
  private:
   const TaskScheduler* task_scheduler_ = nullptr;
 
   DISALLOW_COPY_AND_ASSIGN(ScopedAsyncTaskScheduler);
 };
 
 }  // namespace test
 }  // namespace base
 
 #endif  // BASE_TEST_SCOPED_ASYNC_TASK_SCHEDULER_H_