Fix a few mutability warnings

src/components/gfx/display_list.rs

@@ -96,7 +96,7 @@ impl StackingContext {
     /// Creates a stacking context from a display list.
     fn new(list: DisplayList) -> StackingContext {
         let DisplayList {
-            list: mut list
+            list: list
         } = list;
 
         let mut stacking_context = StackingContext {
@@ -160,7 +160,7 @@ impl StackingContext {
             block_backgrounds_and_borders,
             floats,
             content,
-            positioned_descendants: mut positioned_descendants
+            positioned_descendants: positioned_descendants
         } = other;
 
         let push = |destination: &mut DisplayList, source: DisplayList, level| {

src/components/main/layout/flow.rs

@@ -581,7 +581,7 @@ impl Descendants {
     /// Push the given descendants on to the existing descendants.
     ///
     /// Ignore any static y offsets, because they are None before layout.
-    pub fn push_descendants(&mut self, mut given_descendants: Descendants) {
+    pub fn push_descendants(&mut self, given_descendants: Descendants) {
         for elem in given_descendants.descendant_links.move_iter() {
             self.descendant_links.push(elem);
         }

src/components/main/layout/inline.rs

@@ -1057,7 +1057,7 @@ impl FragmentMap {
     /// necessary.
     fn push_all(&mut self, other: FragmentMap, adjustment: uint) {
         let FragmentMap {
-            list: mut other_list
+            list: other_list
         } = other;
 
         for other_range in other_list.move_iter() {
@@ -1097,7 +1097,7 @@ impl FragmentMap {
     /// needlessly has to clone boxes.
     pub fn fixup(&mut self, old_fragments: &[Box], new_fragments: &[Box]) {
         // TODO(pcwalton): Post Rust upgrade, use `with_capacity` here.
-        let mut old_list = mem::replace(&mut self.list, Vec::new());
+        let old_list = mem::replace(&mut self.list, Vec::new());
         let mut worklist = Vec::new();        // FIXME(#2269, pcwalton): was smallvec4
         let mut old_list_iter = old_list.move_iter().peekable();
         let mut new_fragments_iter = new_fragments.iter().enumerate().peekable();