device: Cleanup class/struct forward declarations

device/hid/hid_service_mac.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_MAC_H_
 #define DEVICE_HID_HID_SERVICE_MAC_H_
 
 #include <CoreFoundation/CoreFoundation.h>
 #include <IOKit/IOKitLib.h>
 
 #include <string>
 
 #include "base/mac/foundation_util.h"
 #include "base/mac/scoped_ionotificationportref.h"
 #include "base/mac/scoped_ioobject.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "device/hid/hid_service.h"
 
 namespace base {
 class SingleThreadTaskRunner;
 }
 
 namespace device {
 
-class HidConnection;
-
 class HidServiceMac : public HidService {
  public:
   HidServiceMac(scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner);
   ~HidServiceMac() override;
 
   void Connect(const HidDeviceId& device_id,
                const ConnectCallback& connect) override;
 
  private:
   // IOService matching callbacks.
@@ skipping 17 matching lines @@
   // The task runner for the FILE thread of the application using this service
   // on which slow running I/O operations can be performed.
   scoped_refptr<base::SingleThreadTaskRunner> file_task_runner_;
 
   DISALLOW_COPY_AND_ASSIGN(HidServiceMac);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_HID_HID_SERVICE_MAC_H_