Make PointerDeviceObserver use ui::InputDeviceEventObserver on X11

chrome/browser/chromeos/device_hierarchy_observer.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.
-
-#ifndef CHROME_BROWSER_CHROMEOS_DEVICE_HIERARCHY_OBSERVER_H_
-#define CHROME_BROWSER_CHROMEOS_DEVICE_HIERARCHY_OBSERVER_H_
-
-namespace chromeos {
-
-// Observers receive notifications when a device has been added/removed.
-class DeviceHierarchyObserver {
- public:
-  virtual void DeviceHierarchyChanged() = 0;
-
-  // Called when a new device (e.g. an external USB keyboard) is attached or
-  // detached.
-  virtual void DeviceAdded(int device_id) = 0;
-  virtual void DeviceRemoved(int device_id) = 0;
-
- protected:
-  virtual ~DeviceHierarchyObserver() {}
-};
-
-}  // namespace chromeos
-
-#endif  // CHROME_BROWSER_CHROMEOS_DEVICE_HIERARCHY_OBSERVER_H_