ozone: Initialize a subsystem only if necessary.

ui/events/ozone/device/udev/device_manager_udev.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 UI_EVENTS_OZONE_DEVICE_UDEV_DEVICE_MANAGER_UDEV_H_
 #define UI_EVENTS_OZONE_DEVICE_UDEV_DEVICE_MANAGER_UDEV_H_
 
 #include "base/message_loop/message_pump_libevent.h"
 #include "base/observer_list.h"
 #include "ui/events/ozone/device/device_manager.h"
 #include "ui/events/ozone/device/udev/scoped_udev.h"
 
 namespace ui {
 
 class DeviceEvent;
 class DeviceEventObserver;
 
 class DeviceManagerUdev
     : public DeviceManager, base::MessagePumpLibevent::Watcher {
  public:
   DeviceManagerUdev();
   virtual ~DeviceManagerUdev();
 
  private:
   scoped_ptr<DeviceEvent> ProcessMessage(udev_device* device);
 
+  // Creates a device-monitor to look for device add/remove/change events.
+  void CreateMonitor();
+
   // DeviceManager overrides:
   virtual void ScanDevices(DeviceEventObserver* observer) OVERRIDE;
   virtual void AddObserver(DeviceEventObserver* observer) OVERRIDE;
   virtual void RemoveObserver(DeviceEventObserver* observer) OVERRIDE;
 
   // base::MessagePumpLibevent::Watcher overrides:
   virtual void OnFileCanReadWithoutBlocking(int fd) OVERRIDE;
   virtual void OnFileCanWriteWithoutBlocking(int fd) OVERRIDE;
 
   scoped_udev udev_;
   scoped_udev_monitor monitor_;
 
   base::MessagePumpLibevent::FileDescriptorWatcher controller_;
 
   ObserverList<DeviceEventObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(DeviceManagerUdev);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_OZONE_DEVICE_UDEV_DEVICE_MANAGER_UDEV_H_