Change device IDs from unsigned to signed.

ui/events/devices/input_device.cc

Index: ui/events/devices/input_device.cc
diff --git a/ui/events/devices/input_device.cc b/ui/events/devices/input_device.cc
index d57af43165b606199572c727674d06b91ad4f697..d08aa51be7f48a2b09d3dcd2d6bc1c91cbe198e7 100644
--- a/ui/events/devices/input_device.cc
+++ b/ui/events/devices/input_device.cc
@@ -9,13 +9,13 @@
 namespace ui {
 
 // static
-const unsigned int InputDevice::kInvalidId = 0;
+const int InputDevice::kInvalidId = 0;
 
 InputDevice::InputDevice()
     : id(kInvalidId), type(InputDeviceType::INPUT_DEVICE_UNKNOWN) {
 }
 
-InputDevice::InputDevice(unsigned int id, InputDeviceType type)
+InputDevice::InputDevice(int id, InputDeviceType type)
     : id(id), type(type) {
 }