Make it possible to disable udev in linux

content/browser/device_monitor_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.
-
-// This class is used to detect device change and notify base::SystemMonitor
-// on Linux.
-
-#ifndef CONTENT_BROWSER_DEVICE_MONITOR_LINUX_H_
-#define CONTENT_BROWSER_DEVICE_MONITOR_LINUX_H_
-
-#include "base/basictypes.h"
-#include "base/memory/scoped_ptr.h"
-#include "base/message_loop/message_loop.h"
-
-extern "C" {
-struct udev_device;
-}
-
-namespace content {
-
-class UdevLinux;
-
-class DeviceMonitorLinux : public base::MessageLoop::DestructionObserver {
- public:
-  DeviceMonitorLinux();
-  virtual ~DeviceMonitorLinux();
-
- private:
-  // This object is deleted on the UI thread after the IO thread has been
-  // destroyed. Need to know when IO thread is being destroyed so that
-  // we can delete udev_.
-  virtual void WillDestroyCurrentMessageLoop() OVERRIDE;
-
-  void Initialize();
-  void OnDevicesChanged(udev_device* device);
-
-  scoped_ptr<UdevLinux> udev_;
-
-  DISALLOW_COPY_AND_ASSIGN(DeviceMonitorLinux);
-};
-
-}  // namespace content
-
-#endif  // CONTENT_BROWSER_DEVICE_MONITOR_LINUX_H_