base: Cleanup class/struct forward declarations

base/threading/worker_pool.h

 // Copyright (c) 2012 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_THREADING_WORKER_POOL_H_
 #define BASE_THREADING_WORKER_POOL_H_
 
 #include "base/base_export.h"
 #include "base/callback_forward.h"
 #include "base/memory/ref_counted.h"
 
-class Task;
-
 namespace tracked_objects {
 class Location;
 }  // namespace tracked_objects
 
 namespace base {
 
 class TaskRunner;
 
 // This is a facility that runs tasks that don't require a specific thread or
 // a message loop.
@@ skipping 27 matching lines @@
   static bool RunsTasksOnCurrentThread();
 
   // Get a TaskRunner wrapper which posts to the WorkerPool using the given
   // |task_is_slow| behavior.
   static const scoped_refptr<TaskRunner>& GetTaskRunner(bool task_is_slow);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_WORKER_POOL_H_