Fix a -Wunused-private-member warning in a //media/gpu file.

media/gpu/generic_v4l2_device.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.
 //
 // This file contains the implementation of GenericV4L2Device used on
 // platforms, which provide generic V4L2 video codec devices.
 
 #ifndef MEDIA_GPU_GENERIC_V4L2_DEVICE_H_
 #define MEDIA_GPU_GENERIC_V4L2_DEVICE_H_
 
@@ skipping 46 matching lines @@
  private:
   ~GenericV4L2Device() override;
 
   // The actual device fd.
   base::ScopedFD device_fd_;
 
   // eventfd fd to signal device poll thread when its poll() should be
   // interrupted.
   base::ScopedFD device_poll_interrupt_fd_;
 
+#if USE_LIBV4L2
   // Use libv4l2 when operating |device_fd_|.
   bool use_libv4l2_;
+#endif
 
   DISALLOW_COPY_AND_ASSIGN(GenericV4L2Device);
 
   // Lazily initialize static data after sandbox is enabled.  Return false on
   // init failure.
   static bool PostSandboxInitialization();
 };
 }  //  namespace media
 
 #endif  // MEDIA_GPU_GENERIC_V4L2_DEVICE_H_