Make SerialIoHandlerWin::UiThreadHelper final.

device/serial/serial_io_handler_win.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_SERIAL_SERIAL_IO_HANDLER_WIN_H_
 #define DEVICE_SERIAL_SERIAL_IO_HANDLER_WIN_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop/message_loop.h"
 #include "base/single_thread_task_runner.h"
@@ skipping 48 matching lines @@
   // Asynchronous event mask state
   DWORD event_mask_;
 
   // Indicates if a pending read is waiting on initial data arrival via
   // WaitCommEvent, as opposed to waiting on actual ReadFile completion
   // after a corresponding WaitCommEvent has completed.
   bool is_comm_pending_;
 
   // The helper lives on the UI thread and holds a weak reference back to the
   // handler that owns it.
-  UiThreadHelper* helper_ = nullptr;
+  UiThreadHelper* helper_;
   base::WeakPtrFactory<SerialIoHandlerWin> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SerialIoHandlerWin);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_SERIAL_SERIAL_IO_HANDLER_WIN_H_