IDL: make optional arguments (without default) explicit sometimes

Source/core/storage/StorageEvent.idl

Index: Source/core/storage/StorageEvent.idl
diff --git a/Source/core/storage/StorageEvent.idl b/Source/core/storage/StorageEvent.idl
index 39801af564ea78c6e0bee029877bdd9931e4a468..1154b9d3ac91a724f2c49ae86c16274a325c37be 100644
--- a/Source/core/storage/StorageEvent.idl
+++ b/Source/core/storage/StorageEvent.idl
@@ -32,14 +32,14 @@
     [InitializedByEventConstructor] readonly attribute DOMString url;
     [InitializedByEventConstructor] readonly attribute Storage? storageArea;
 
-    void initStorageEvent([Default=Undefined] optional DOMString typeArg,
-                          [Default=Undefined] optional boolean canBubbleArg,
-                          [Default=Undefined] optional boolean cancelableArg,
-                          [Default=Undefined] optional DOMString keyArg,
-                          [Default=Undefined] optional DOMString? oldValueArg,
-                          [Default=Undefined] optional DOMString? newValueArg,
-                          [Default=Undefined] optional DOMString urlArg,
-                          [Default=Undefined] optional Storage storageAreaArg);
+    void initStorageEvent(optional DOMString typeArg,
+                          optional boolean canBubbleArg,
+                          optional boolean cancelableArg,
+                          optional DOMString keyArg,
+                          optional DOMString? oldValueArg,
+                          optional DOMString? newValueArg,
+                          optional DOMString urlArg,
+                          optional Storage storageAreaArg);
 
     // Needed once we support init<blank>EventNS
     // void initStorageEventNS(DOMString namespaceURI, DOMString typeArg, boolean canBubbleArg, boolean cancelableArg, DOMString keyArg, DOMString oldValueArg, DOMString newValueArg, DOMString urlArg, Storage storageAreaArg);