Change device IDs from unsigned to signed.

ui/events/devices/input_device.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_DEVICES_INPUT_DEVICE_H_
 #define UI_EVENTS_DEVICES_INPUT_DEVICE_H_
 
 #include <string>
 
 #include "ui/events/devices/events_devices_export.h"
 
 namespace ui {
 
 enum InputDeviceType {
   INPUT_DEVICE_INTERNAL,  // Internally connected input device.
   INPUT_DEVICE_EXTERNAL,  // Known externally connected input device.
   INPUT_DEVICE_UNKNOWN,   // Device that may or may not be an external device.
 };
 
 // Represents an input device state.
 struct EVENTS_DEVICES_EXPORT InputDevice {
-  static const unsigned int kInvalidId;
+  static const int kInvalidId;
 
   // Creates an invalid input device.
   InputDevice();
 
-  InputDevice(unsigned int id, InputDeviceType type);
+  InputDevice(int id, InputDeviceType type);
   virtual ~InputDevice();
 
   // ID of the device. This ID is unique between all input devices.
-  unsigned int id;
+  int id;
 
   // The type of the input device.
   InputDeviceType type;
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_DEVICES_INPUT_DEVICE_H_