Remove SingleThreadTaskRunner Support from SchedulerWorkerPoolImpl

base/task_scheduler/priority_queue.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_PRIORITY_QUEUE_H_
 #define BASE_TASK_SCHEDULER_PRIORITY_QUEUE_H_
 
 #include <memory>
 #include <queue>
 #include <vector>
@@ skipping 52 matching lines @@
     // Holds the lock of |outer_queue_| for the lifetime of this Transaction.
     AutoSchedulerLock auto_lock_;
 
     PriorityQueue* const outer_queue_;
 
     DISALLOW_COPY_AND_ASSIGN(Transaction);
   };
 
   PriorityQueue();
 
-  // |predecessor_priority_queue| is a PriorityQueue for which a thread is
-  // allowed to have an active Transaction when it creates a Transaction for
-  // this PriorityQueue.
-  PriorityQueue(const PriorityQueue* predecessor_priority_queue);
-
   ~PriorityQueue();
 
   // Begins a Transaction. This method cannot be called on a thread which has an
   // active Transaction unless the last Transaction created on the thread was
   // for the allowed predecessor specified in the constructor of this
   // PriorityQueue.
   std::unique_ptr<Transaction> BeginTransaction();
 
   const SchedulerLock* container_lock() const { return &container_lock_; }
 
  private:
   // A class combining a Sequence and the SequenceSortKey that determines its
   // position in a PriorityQueue.
   class SequenceAndSortKey;
 
   using ContainerType = std::priority_queue<SequenceAndSortKey>;
 
   // Synchronizes access to |container_|.
   SchedulerLock container_lock_;
 
   ContainerType container_;
 
   DISALLOW_COPY_AND_ASSIGN(PriorityQueue);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_PRIORITY_QUEUE_H_