Sync ui/events to chromium @ https://codereview.chromium.org/1210203002

ui/events/device_hotplug_event_observer.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_DEVICE_HOTPLUG_EVENT_OBSERVER_H_
-#define UI_EVENTS_DEVICE_HOTPLUG_EVENT_OBSERVER_H_
-
-#include "ui/events/events_base_export.h"
-#include "ui/events/touchscreen_device.h"
-
-namespace ui {
-
-// Listener for specific input device hotplug events.
-class EVENTS_BASE_EXPORT DeviceHotplugEventObserver {
- public:
-  virtual ~DeviceHotplugEventObserver() {}
-
-  // On a hotplug event this is called with the list of available devices.
-  virtual void OnTouchscreenDevicesUpdated(
-      const std::vector<TouchscreenDevice>& devices) = 0;
-};
-
-}  // namespace ui
-
-#endif  // UI_EVENTS_DEVICE_HOTPLUG_EVENT_OBSERVER_H_