[TaskScheduler] Support TaskRunnerHandles from parallel tasks.

base/task_scheduler/scheduler_thread_pool.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_SCHEDULER_THREAD_POOL_H_
 #define BASE_TASK_SCHEDULER_SCHEDULER_THREAD_POOL_H_
 
 #include <memory>
 
 #include "base/base_export.h"
@@ skipping 27 matching lines @@
   // SchedulerThreadPool.
   virtual void ReEnqueueSequence(scoped_refptr<Sequence> sequence,
                                  const SequenceSortKey& sequence_sort_key) = 0;
 
   // Posts |task| to be executed by this SchedulerThreadPool as part of
   // |sequence|. If |worker_thread| is non-null, |task| will be scheduled to run
   // on it specifically (note: |worker_thread| must be owned by this
   // SchedulerThreadPool); otherwise, |task| will be added to the pending shared
   // work. |task| won't be executed before its delayed run time, if any. Returns
   // true if |task| is posted.
+  //FIXME: Remove from public interface?
   virtual bool PostTaskWithSequence(std::unique_ptr<Task> task,
                                     scoped_refptr<Sequence> sequence,
                                     SchedulerWorkerThread* worker_thread) = 0;
 
   // Posts |task| to be executed by this SchedulerThreadPool as part of
   // |sequence|. If |worker_thread| is non-null, |task| will be scheduled to run
   // on it specifically (note: |worker_thread| must be owned by this
   // SchedulerThreadPool); otherwise, |task| will be added to the pending shared
   // work. This must only be called after |task| has gone through
   // PostTaskWithSequence() and after |task|'s delayed run time.
   virtual void PostTaskWithSequenceNow(
       std::unique_ptr<Task> task,
       scoped_refptr<Sequence> sequence,
       SchedulerWorkerThread* worker_thread) = 0;
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_SCHEDULER_THREAD_POOL_H_