Auto merge of #27163 - alarsyo:23053-layout-queries-disconnected-frames-panic, r=jdm

Return Option for Window's layout channel

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`Window::layout_chan()` now returns an `Option<Sender<Msg>>`, returning `None` if the window is dead.

FIX #26969
FIX #26429
FIX #21208
FIX #19092
FIX #22559
FIX #22584
FIX #22652

---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #23053

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- [x] There are tests for these changes

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This is my first contribution, I'm trying to figure things out!

This fix passes the test case shown in #23053, however I don't know what the behavior should be in `Document` and `ScriptThread` if `Window::is_alive()` is false : simply ignore it, don't do anything ? Or is this something that should not happen now that we return false in `Window::force_reflow()` ?

I'm not sure about the directory where the test case should go, any advice?

components/script/script_thread.rs

@@ -1172,9 +1172,13 @@ impl ScriptThread {
                 );
             },
         };
-        let _ = window
-            .layout_chan()
-            .send(Msg::RegisterPaint(name, properties, painter));
+
+        match window.layout_chan() {
+            Some(chan) => chan
+                .send(Msg::RegisterPaint(name, properties, painter))
+                .unwrap(),
+            None => warn!("Layout channel unavailable"),
+        }
     }
 
     pub fn push_new_element_queue() {
@@ -2467,12 +2471,12 @@ impl ScriptThread {
         });
 
         // Pick a layout thread, any layout thread
-        let current_layout_chan = self
+        let current_layout_chan: Option<Sender<Msg>> = self
             .documents
             .borrow()
             .iter()
             .next()
-            .map(|(_, document)| document.window().layout_chan().clone())
+            .and_then(|(_, document)| document.window().layout_chan().cloned())
             .or_else(|| {
                 self.incomplete_loads
                     .borrow()
@@ -2879,7 +2883,10 @@ impl ScriptThread {
             let load = self.incomplete_loads.borrow_mut().remove(idx);
             load.layout_chan.clone()
         } else if let Some(ref document) = document {
-            document.window().layout_chan().clone()
+            match document.window().layout_chan() {
+                Some(chan) => chan.clone(),
+                None => return warn!("Layout channel unavailable"),
+            }
         } else {
             return warn!("Exiting nonexistant pipeline {}.", id);
         };