script: Expose NodeTraits::owner_global / Window::as_global_scope (#34843)

Expose two new helpers and start using them as much as possible.

- `NodeTraits::owner_global`: which gets the `GlobalScope` that currenty
 owns a `Node`. This may be different than `.global()` in the case that
 the `Node` was adopted by a different `Document`.
- `Window::as_global_scope`: A helper to avoid having to cast so much
  when treating a `Window` like a `GlobalScope`.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/script/dom/userscripts.rs

@@ -9,10 +9,8 @@ use std::rc::Rc;
 
 use js::jsval::UndefinedValue;
 
-use crate::dom::bindings::inheritance::Castable;
 use crate::dom::bindings::refcounted::Trusted;
 use crate::dom::bindings::str::DOMString;
-use crate::dom::globalscope::GlobalScope;
 use crate::dom::htmlheadelement::HTMLHeadElement;
 use crate::dom::htmlscriptelement::SourceCode;
 use crate::dom::node::NodeTraits;
@@ -25,9 +23,9 @@ pub fn load_script(head: &HTMLHeadElement) {
         Some(p) => p,
         None => return,
     };
-    let win = Trusted::new(doc.window());
+    let window = Trusted::new(doc.window());
     doc.add_delayed_task(task!(UserScriptExecute: move || {
-        let win = win.root();
+        let win = window.root();
         let cx = win.get_cx();
         rooted!(in(*cx) let mut rval = UndefinedValue());
 
@@ -47,14 +45,15 @@ pub fn load_script(head: &HTMLHeadElement) {
             let script_text = SourceCode::Text(
                 Rc::new(DOMString::from_string(String::from_utf8_lossy(&contents).to_string()))
             );
-            let global = win.upcast::<GlobalScope>();
-            global.evaluate_script_on_global_with_result(
+
+            let global_scope = win.as_global_scope();
+            global_scope.evaluate_script_on_global_with_result(
                 &script_text,
                 &file.to_string_lossy(),
                 rval.handle_mut(),
                 1,
-                ScriptFetchOptions::default_classic_script(global),
-                global.api_base_url(),
+                ScriptFetchOptions::default_classic_script(global_scope),
+                global_scope.api_base_url(),
                 CanGc::note(),
             );
         }