Move touchscreen device caching to DeviceDataManager

ui/events/input_device_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_INPUT_DEVICE_EVENT_OBSERVER_H_
+#define UI_EVENTS_INPUT_DEVICE_EVENT_OBSERVER_H_
+
+namespace ui {
+
+// DeviceDataManager observer used to announce input hotplug events.
+class InputDeviceEventObserver {
+ public:
+  virtual ~InputDeviceEventObserver() {}
+
+  virtual void OnInputDeviceConfigurationChanged() = 0;
+};
+
+}  // namespace ui
+
+#endif  // UI_EVENTS_INPUT_DEVICE_EVENT_OBSERVER_H_