Remove use of unstable box syntax.

http://www.robohornet.org gives a score of 101.36 on master,
and 102.68 with this PR. The latter is slightly better,
but probably within noise level.
So it looks like this PR does not affect DOM performance.

This is expected since `Box::new` is defined as:

```rust
impl<T> Box<T> {
    #[inline(always)]
    pub fn new(x: T) -> Box<T> {
        box x
    }
}
```

With inlining, it should compile to the same as box syntax.

1 files changed, 3 insertions, 3 deletions

diff --git a/components/script/dom/xmlhttprequest.rs b/components/script/dom/xmlhttprequest.rs
index 4b9b2b45a4c..2baa7351034 100644
--- a/components/script/dom/xmlhttprequest.rs
+++ b/components/script/dom/xmlhttprequest.rs
@@ -204,7 +204,7 @@ impl XMLHttpRequest {
         }
     }
     pub fn new(global: &GlobalScope) -> DomRoot<XMLHttpRequest> {
-        reflect_dom_object(box XMLHttpRequest::new_inherited(global),
+        reflect_dom_object(Box::new(XMLHttpRequest::new_inherited(global)),
                            global,
                            XMLHttpRequestBinding::Wrap)
     }
@@ -263,9 +263,9 @@ impl XMLHttpRequest {
             task_source: task_source,
             canceller: Some(global.task_canceller())
         };
-        ROUTER.add_route(action_receiver.to_opaque(), box move |message| {
+        ROUTER.add_route(action_receiver.to_opaque(), Box::new(move |message| {
             listener.notify_fetch(message.to().unwrap());
-        });
+        }));
         global.core_resource_thread().send(Fetch(init, action_sender)).unwrap();
     }
 }