base: Cleanup class/struct forward declarations

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 12 matching lines @@
 #include "base/threading/thread.h"
 
 namespace base {
 
 class HistogramBase;
 class SchedulerWorkerPoolParams;
 
 namespace internal {
 
 class DelayedTaskManager;
-class SchedulerServiceThread;
 class TaskTracker;
 
 // Default TaskScheduler implementation. This class is thread-safe.
 class BASE_EXPORT TaskSchedulerImpl : public TaskScheduler {
  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(
@@ skipping 49 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_