Make use of RefCell::try_borrow_unguarded

components/script/dom/bindings/cell.rs

@@ -26,7 +26,9 @@ impl<T> DomRefCell<T> {
     #[allow(unsafe_code)]
     pub unsafe fn borrow_for_layout(&self) -> &T {
         debug_assert!(thread_state::get().is_layout());
-        &*self.value.as_ptr()
+        self.value
+            .try_borrow_unguarded()
+            .expect("cell is mutably borrowed")
     }
 
     /// Borrow the contents for the purpose of script deallocation.

components/script/dom/xmlhttprequest.rs

@@ -1442,8 +1442,6 @@ impl XMLHttpRequest {
 
     fn filter_response_headers(&self) -> HeaderMap {
         // https://fetch.spec.whatwg.org/#concept-response-header-list
-        use http::header::{self, HeaderName};
-
         let mut headers = self.response_headers.borrow().clone();
         headers.remove(header::SET_COOKIE);
         headers.remove(HeaderName::from_static("set-cookie2"));

components/script/lib.rs

@@ -4,6 +4,7 @@
 
 #![cfg_attr(feature = "unstable", feature(core_intrinsics))]
 #![cfg_attr(feature = "unstable", feature(on_unimplemented))]
+#![feature(borrow_state)]
 #![feature(const_fn)]
 #![feature(drain_filter)]
 #![feature(inner_deref)]