Auto merge of #27016 - gterzian:fix_closing_window, r=jdm,paulrouget

Ensure clean shutdown of JS threads

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FIX https://github.com/servo/servo/issues/26685
FIX https://github.com/servo/servo/issues/26996
FIX https://github.com/servo/servo/issues/9672
FIX #27027

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- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #___ (GitHub issue number if applicable)

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components/servo/lib.rs

@@ -1063,11 +1063,7 @@ pub fn run_content_process(token: String) {
 
             set_logger(content.script_to_constellation_chan().clone());
 
-            let background_hang_monitor_register = if opts::get().background_hang_monitor {
-                content.register_with_background_hang_monitor()
-            } else {
-                None
-            };
+            let background_hang_monitor_register = content.register_with_background_hang_monitor();
 
             content.start_all::<script_layout_interface::message::Msg,
                                              layout_thread::LayoutThread,