Make Document::root private, in preparation for removing it as part of making Document a Node.

src/components/script/dom/node.rs

@@ -417,7 +417,7 @@ impl<'self, View> AbstractNode<View> {
     pub fn is_in_doc(&self) -> bool {
         do self.with_base |node| {
             do node.owner_doc.with_base |document| {
-                match document.root {
+                match document.GetDocumentElement() {
                     None => false,
                     Some(root) => {
                         let mut node = *self;