device: Cleanup class/struct forward declarations

device/udev_linux/udev_linux.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.
 
 // UdevLinux listens for device change notifications from udev and runs
 // callbacks when notifications occur.
 //
 // UdevLinux must be created on a thread that has instantiated a
 // FileDescriptorWatcher. UdevLinux is not thread-safe.
 //
@@ skipping 30 matching lines @@
 
 #include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/files/file_descriptor_watcher_posix.h"
 #include "base/macros.h"
 #include "device/udev_linux/scoped_udev.h"
 
 extern "C" {
 struct udev;
 struct udev_device;
-struct udev_monitor;
 }
 
 namespace device {
 
 class UdevLinux {
  public:
   typedef base::Callback<void(udev_device*)> UdevNotificationCallback;
 
   // subsystem and devtype parameter for
   // udev_monitor_filter_add_match_subsystem_devtype().
@@ skipping 25 matching lines @@
   std::unique_ptr<base::FileDescriptorWatcher::Controller>
       monitor_watch_controller_;
   const UdevNotificationCallback callback_;
 
   DISALLOW_COPY_AND_ASSIGN(UdevLinux);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_UDEV_LINUX_UDEV_LINUX_H_