Pass the prefix to Element::new in create_element.

components/script/dom/create.rs

@@ -83,7 +83,7 @@ pub fn create_element(name: QualName, prefix: Option<DOMString>,
                       document: JSRef<Document>, creator: ElementCreator)
                       -> Temporary<Element> {
     if name.ns != ns!(HTML) {
-        return Element::new(name.local.as_slice().to_string(), name.ns, None, document);
+        return Element::new(name.local.as_slice().to_string(), name.ns, prefix, document);
     }
 
     macro_rules! make(

tests/wpt/metadata/dom/nodes/Node-cloneNode.html.ini

@@ -1,5 +0,0 @@
-[Node-cloneNode.html]
-  type: testharness
-  [Prefixed non-HTML element]
-    expected: FAIL
-