Remove unnecessary mutability.

src/components/script/dom/document.rs

@@ -117,7 +117,7 @@ impl Document {
     pub fn Constructor(owner: @mut Window) -> Fallible<AbstractDocument> {
         let cx = owner.page.js_info.get_ref().js_compartment.cx.ptr;
 
-        let mut document = AbstractDocument::as_abstract(cx, @mut Document::new(None, XML));
+        let document = AbstractDocument::as_abstract(cx, @mut Document::new(None, XML));
 
         let root = @HTMLHtmlElement {
             htmlelement: HTMLElement::new(HTMLHtmlElementTypeId, ~"html")

src/components/script/dom/domparser.rs

@@ -42,7 +42,7 @@ impl DOMParser {
                            ty: DOMParserBinding::SupportedType)
                            -> Fallible<AbstractDocument> {
         let cx = (*self.owner.page).js_info.get_ref().js_compartment.cx.ptr;
-        let mut document = match ty {
+        let document = match ty {
             Text_html => {
                 HTMLDocument::new(None)
             }

src/components/script/script_task.rs

@@ -722,7 +722,7 @@ impl ScriptTask {
                                                                  page.next_subpage_id.clone(),
                                                                  self.constellation_chan.clone());
 
-        let mut document = HTMLDocument::new(Some(window));
+        let document = HTMLDocument::new(Some(window));
 
         let HtmlParserResult {root, discovery_port, url: final_url} = html_parsing_result;
         document.set_root(root);