IDL: make optional arguments (without default) explicit sometimes

Source/core/events/MutationEvent.idl

Index: Source/core/events/MutationEvent.idl
diff --git a/Source/core/events/MutationEvent.idl b/Source/core/events/MutationEvent.idl
index 0aae4e31df94247d75cf26a374294aae883f39cc..41bf45791a57349d04f715aefdc465899748ecea 100644
--- a/Source/core/events/MutationEvent.idl
+++ b/Source/core/events/MutationEvent.idl
@@ -31,14 +31,14 @@ interface MutationEvent : Event {
     readonly attribute DOMString      attrName;
     readonly attribute unsigned short attrChange;
 
-     void initMutationEvent([Default=Undefined] optional DOMString type,
-                                          [Default=Undefined] optional boolean canBubble,
-                                          [Default=Undefined] optional boolean cancelable,
-                                          [Default=Undefined] optional Node relatedNode,
-                                          [Default=Undefined] optional DOMString prevValue,
-                                          [Default=Undefined] optional DOMString newValue,
-                                          [Default=Undefined] optional DOMString attrName,
-                                          [Default=Undefined] optional unsigned short attrChange);
+     void initMutationEvent(optional DOMString type,
+                                          optional boolean canBubble,
+                                          optional boolean cancelable,
+                                          optional Node relatedNode,
+                                          optional DOMString prevValue,
+                                          optional DOMString newValue,
+                                          optional DOMString attrName,
+                                          optional unsigned short attrChange);
 
 };