Fix "unused variable" warnings.

device/usb/usb_device_handle_usbfs.h

 // Copyright 2016 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_USB_USB_DEVICE_HANDLE_USBFS_H_
 #define DEVICE_USB_USB_DEVICE_HANDLE_USBFS_H_
 
 #include <list>
 #include <map>
 #include <memory>
@@ skipping 119 matching lines @@
       const UsbDeviceHandle::IsochronousTransferCallback& callback,
       UsbTransferStatus status);
   void SetUpTimeoutCallback(Transfer* transfer, unsigned int timeout);
 
   static void CancelTransfer(Transfer* transfer, UsbTransferStatus status);
 
   scoped_refptr<UsbDevice> device_;
   base::ScopedFD fd_;
   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
   scoped_refptr<base::SequencedTaskRunner> blocking_task_runner_;
-  base::ThreadChecker thread_checker_;
 
   // Maps claimed interfaces by interface number to their current alternate
   // setting.
   std::map<uint8_t, InterfaceInfo> interfaces_;
 
   // Maps endpoints (by endpoint address) to the interface they are a part of.
   // Only endpoints of currently claimed and selected interface alternates are
   // included in the map.
   std::map<uint8_t, EndpointInfo> endpoints_;
 
   // Helper object owned by the blocking task thread. It will be freed if that
   // thread's message loop is destroyed but can also be freed by this class on
   // destruction.
   FileThreadHelper* helper_;
 
   std::list<std::unique_ptr<Transfer>> transfers_;
 };
 
 }  // namespace device
 
 #endif  // DEVICE_USB_USB_DEVICE_HANDLE_USBFS_H_