Change device IDs from unsigned to signed.

ui/events/devices/input_device.h

Index: ui/events/devices/input_device.h
diff --git a/ui/events/devices/input_device.h b/ui/events/devices/input_device.h
index 70ae1924007306044af33db0ebb4c624ef171068..ee493eadea15044abfc768e4857e7acc1e5ed5d0 100644
--- a/ui/events/devices/input_device.h
+++ b/ui/events/devices/input_device.h
@@ -19,16 +19,16 @@ enum InputDeviceType {
 
 // 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;