device: Cleanup class/struct forward declarations

device/hid/hid_service_linux.h

 // Copyright 2014 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 DEVICE_HID_HID_SERVICE_LINUX_H_
 #define DEVICE_HID_HID_SERVICE_LINUX_H_
 
 #include <memory>
 
 #include "base/compiler_specific.h"
 #include "base/files/scoped_file.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "build/build_config.h"
 #include "device/hid/hid_device_info.h"
 #include "device/hid/hid_service.h"
 
 namespace device {
 
-class HidConnection;
-
 class HidServiceLinux : public HidService {
  public:
   HidServiceLinux(scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner);
   ~HidServiceLinux() override;
 
   // HidService:
   void Shutdown() override;
   void Connect(const HidDeviceId& device_id,
                const ConnectCallback& callback) override;
 
@@ skipping 25 matching lines @@
   // service that owns it.
   std::unique_ptr<FileThreadHelper> helper_;
   base::WeakPtrFactory<HidServiceLinux> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(HidServiceLinux);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_HID_HID_SERVICE_LINUX_H_