Sync DOMImplementation.createDocument() IDL with spec

Source/core/dom/DOMImplementation.idl

Index: Source/core/dom/DOMImplementation.idl
diff --git a/Source/core/dom/DOMImplementation.idl b/Source/core/dom/DOMImplementation.idl
index d210529988b3d61554dfd7ed7a953699b0ea9b3c..327543a03d4e729cc9ff63ff164f170db8fcb66a 100644
--- a/Source/core/dom/DOMImplementation.idl
+++ b/Source/core/dom/DOMImplementation.idl
@@ -20,6 +20,7 @@
 
 [
     SetWrapperReferenceFrom=document,
+    TypeChecking=Interface,
     WillBeGarbageCollected,
 ] interface DOMImplementation {
 
@@ -34,8 +35,8 @@
                                                       DOMString publicId,
                                                       DOMString systemId);
     [RaisesException] XMLDocument createDocument(DOMString? namespaceURI,
-                                                 DOMString? qualifiedName,
-                                                 [Default=Undefined] optional DocumentType doctype);
+                                                 [TreatNullAs=EmptyString] DOMString qualifiedName,
+                                                 optional DocumentType? doctype = null);
 
     // HTMLDOMImplementation interface from DOM Level 2 HTML