Adds borrow_for_script_deallocation and unsafe_mut_js_info method to avoid 'DOMRefCell already mutably borrowed' messages. This is just a temporary fix until the Rust standard library allows borrowing already-borrowed RefCell values during unwinding.

It also removes LiveDOMReferences destructor that it's a no-op but it contains an assert that was being violated causing an endless cycle of destructor calls ending up in a stack overflow.

components/script/page.rs

@@ -273,6 +273,10 @@ impl Page {
         self.js_info.borrow_mut()
     }
 
+    pub unsafe fn unsafe_mut_js_info<'a>(&'a self) -> &'a mut Option<JSPageInfo> {
+        self.js_info.borrow_for_script_deallocation()
+    }
+
     pub fn js_info<'a>(&'a self) -> Ref<'a, Option<JSPageInfo>> {
         self.js_info.borrow()
     }