Remove warnings about unnecessary mutability.

components/script/dom/extendablemessageevent.rs

@@ -17,7 +17,6 @@ use dom::serviceworkerglobalscope::ServiceWorkerGlobalScope;
 use js::jsapi::{HandleValue, Heap, JSContext};
 use js::jsval::JSVal;
 use servo_atoms::Atom;
-use std::default::Default;
 
 #[dom_struct]
 pub struct ExtendableMessageEvent {
@@ -32,13 +31,12 @@ impl ExtendableMessageEvent {
                bubbles: bool, cancelable: bool,
                data: HandleValue, origin: DOMString, lastEventId: DOMString)
                -> Root<ExtendableMessageEvent> {
-        let mut ev = box ExtendableMessageEvent {
+        let ev = box ExtendableMessageEvent {
             event: ExtendableEvent::new_inherited(),
-            data: Heap::default(),
+            data: Heap::new(data.get()),
             origin: origin,
             lastEventId: lastEventId,
         };
-        ev.data.set(data.get());
         let ev = reflect_dom_object(ev, global, ExtendableMessageEventBinding::Wrap);
         {
             let event = ev.upcast::<Event>();

components/script/dom/imagedata.rs

@@ -27,7 +27,7 @@ pub struct ImageData {
 impl ImageData {
     #[allow(unsafe_code)]
     pub fn new(global: &GlobalScope, width: u32, height: u32, data: Option<Vec<u8>>) -> Root<ImageData> {
-        let mut imagedata = box ImageData {
+        let imagedata = box ImageData {
             reflector_: Reflector::new(),
             width: width,
             height: height,

components/script/dom/messageevent.rs

@@ -16,7 +16,6 @@ use dom::globalscope::GlobalScope;
 use js::jsapi::{HandleValue, Heap, JSContext};
 use js::jsval::JSVal;
 use servo_atoms::Atom;
-use std::default::Default;
 
 #[dom_struct]
 pub struct MessageEvent {
@@ -38,13 +37,12 @@ impl MessageEvent {
                            data: HandleValue,
                            origin: DOMString,
                            lastEventId: DOMString) -> Root<MessageEvent> {
-        let mut ev = box MessageEvent {
+        let ev = box MessageEvent {
             event: Event::new_inherited(),
-            data: Heap::default(),
+            data: Heap::new(data.get()),
             origin: origin,
             lastEventId: lastEventId,
         };
-        ev.data.set(data.get());
         reflect_dom_object(ev, global, MessageEventBinding::Wrap)
     }
 

components/script/dom/vreyeparameters.rs

@@ -31,7 +31,7 @@ impl VREyeParameters {
     #[allow(unrooted_must_root)]
     fn new_inherited(parameters: WebVREyeParameters, global: &GlobalScope) -> VREyeParameters {
         let fov = VRFieldOfView::new(&global, parameters.field_of_view.clone());
-        let mut result = VREyeParameters {
+        let result = VREyeParameters {
             reflector_: Reflector::new(),
             parameters: DOMRefCell::new(parameters),
             offset: Heap::default(),

components/script/dom/vrframedata.rs

@@ -39,7 +39,7 @@ impl VRFrameData {
                       0.0, 0.0, 0.0, 1.0f32];
         let pose = VRPose::new(&global, &Default::default());
 
-        let mut framedata = VRFrameData {
+        let framedata = VRFrameData {
             reflector_: Reflector::new(),
             left_proj: Heap::default(),
             left_view: Heap::default(),

components/script/dom/vrpose.rs

@@ -29,7 +29,7 @@ pub struct VRPose {
 unsafe fn update_or_create_typed_array(cx: *mut JSContext,
                       src: Option<&[f32]>,
                       dst: &DOMRefCell<Heap<*mut JSObject>>) {
-    let mut dst = dst.borrow_mut();
+    let dst = dst.borrow();
     match src {
         Some(ref data) => {
             if dst.get().is_null() {

components/script/dom/vrstageparameters.rs

@@ -28,7 +28,7 @@ impl VRStageParameters {
     #[allow(unsafe_code)]
     #[allow(unrooted_must_root)]
     fn new_inherited(parameters: WebVRStageParameters, global: &GlobalScope) -> VRStageParameters {
-        let mut stage = VRStageParameters {
+        let stage = VRStageParameters {
             reflector_: Reflector::new(),
             parameters: DOMRefCell::new(parameters),
             transform: Heap::default()