Remove unused include in sequenced_worker_pool.h

components/drive/chromeos/file_system.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 COMPONENTS_DRIVE_CHROMEOS_FILE_SYSTEM_H_
 #define COMPONENTS_DRIVE_CHROMEOS_FILE_SYSTEM_H_
 
 #include <stdint.h>
 
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
+#include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "base/observer_list.h"
 #include "base/threading/thread_checker.h"
 #include "components/drive/chromeos/change_list_loader_observer.h"
 #include "components/drive/chromeos/file_system/operation_delegate.h"
 #include "components/drive/chromeos/file_system_interface.h"
 #include "google_apis/drive/drive_api_error_codes.h"
 
 class PrefService;
 
 namespace base {
 class SequencedTaskRunner;
+class SingleThreadTaskRunner;
 }  // namespace base
 
 namespace google_apis {
 class AboutResource;
 class ResourceEntry;
 }  // namespace google_apis
 
 namespace drive {
 struct ClientContext;
 class EventLogger;
@@ skipping 269 matching lines @@
   // Note: This should remain the last member so it'll be destroyed and
   // invalidate the weak pointers before any other members are destroyed.
   base::WeakPtrFactory<FileSystem> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(FileSystem);
 };
 
 }  // namespace drive
 
 #endif  // COMPONENTS_DRIVE_CHROMEOS_FILE_SYSTEM_H_