Remove unused include in sequenced_worker_pool.h

ipc/attachment_broker.h

 // Copyright 2015 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 IPC_ATTACHMENT_BROKER_H_
 #define IPC_ATTACHMENT_BROKER_H_
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/process/process_handle.h"
+#include "base/single_thread_task_runner.h"
 #include "base/synchronization/lock.h"
 #include "build/build_config.h"
 #include "ipc/brokerable_attachment.h"
 #include "ipc/ipc_export.h"
 #include "ipc/ipc_listener.h"
 
 // If the platform has no attachments that need brokering, then it shouldn't
 // compile any code that calls member functions of AttachmentBroker. This
 // prevents symbols only used by AttachmentBroker and its subclasses from
 // making it into the binary.
@@ skipping 145 matching lines @@
 
   // The AttachmentBroker can be accessed from any thread, so modifications to
   // internal state must be guarded by a lock.
   base::Lock lock_;
   DISALLOW_COPY_AND_ASSIGN(AttachmentBroker);
 };
 
 }  // namespace IPC
 
 #endif  // IPC_ATTACHMENT_BROKER_H_