IDL: make optional arguments (without default) explicit sometimes

Source/modules/device_orientation/DeviceMotionEvent.idl

Index: Source/modules/device_orientation/DeviceMotionEvent.idl
diff --git a/Source/modules/device_orientation/DeviceMotionEvent.idl b/Source/modules/device_orientation/DeviceMotionEvent.idl
index 5e70a8376ab194aa368ce19d2731490d2e31181e..2014a290dc49a6a10cca9727e32026c898024b45 100644
--- a/Source/modules/device_orientation/DeviceMotionEvent.idl
+++ b/Source/modules/device_orientation/DeviceMotionEvent.idl
@@ -28,11 +28,11 @@ interface DeviceMotionEvent : Event {
     readonly attribute DeviceAcceleration accelerationIncludingGravity;
     readonly attribute DeviceRotationRate rotationRate;
     readonly attribute double? interval;
-    [Custom] void initDeviceMotionEvent([Default=Undefined] optional DOMString type,
-                                        [Default=Undefined] optional boolean bubbles,
-                                        [Default=Undefined] optional boolean cancelable,
-                                        [Default=Undefined] optional DeviceAcceleration acceleration,
-                                        [Default=Undefined] optional DeviceAcceleration accelerationIncludingGravity,
-                                        [Default=Undefined] optional DeviceRotationRate rotationRate,
-                                        [Default=Undefined] optional double interval);
+    [Custom] void initDeviceMotionEvent(optional DOMString type,
+                                        optional boolean bubbles,
+                                        optional boolean cancelable,
+                                        optional DeviceAcceleration acceleration,
+                                        optional DeviceAcceleration accelerationIncludingGravity,
+                                        optional DeviceRotationRate rotationRate,
+                                        optional double interval);
 };