auto merge of #4130 : saneyuki/servo/cast, r=Manishearth

Fix #4124

This also introduce `BarCast::from_actual()` which is used for up-cast for dom's actual data types (non JS pointer values).

components/script/dom/htmlelement.rs

@@ -50,11 +50,6 @@ impl HTMLElement {
         let element = HTMLElement::new_inherited(HTMLElementTypeId, localName, prefix, document);
         Node::reflect_node(box element, document, HTMLElementBinding::Wrap)
     }
-
-    #[inline]
-    pub fn element<'a>(&'a self) -> &'a Element {
-        &self.element
-    }
 }
 
 trait PrivateHTMLElementHelpers {