TaskScheduler: Avoid Sequence refcount bump in GetWork()

base/task_scheduler/scheduler_thread_pool_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_SCHEDULER_THREAD_POOL_IMPL_H_
 #define BASE_TASK_SCHEDULER_SCHEDULER_THREAD_POOL_IMPL_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 13 matching lines @@
 #include "base/task_scheduler/scheduler_worker_thread_stack.h"
 #include "base/task_scheduler/sequence.h"
 #include "base/task_scheduler/task.h"
 #include "base/task_scheduler/task_traits.h"
 #include "base/threading/platform_thread.h"
 
 namespace base {
 namespace internal {
 
 class DelayedTaskManager;
-struct SequenceSortKey;
 class TaskTracker;
 
 // A pool of threads that run Tasks. This class is thread-safe.
 class BASE_EXPORT SchedulerThreadPoolImpl : public SchedulerThreadPool {
  public:
   // Callback invoked when a Sequence isn't empty after a worker thread pops a
   // Task from it.
   using ReEnqueueSequenceCallback = Callback<void(scoped_refptr<Sequence>)>;
 
   // Destroying a SchedulerThreadPool returned by CreateThreadPool() is not
@@ skipping 90 matching lines @@
   TaskTracker* const task_tracker_;
   DelayedTaskManager* const delayed_task_manager_;
 
   DISALLOW_COPY_AND_ASSIGN(SchedulerThreadPoolImpl);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_SCHEDULER_THREAD_POOL_IMPL_H_