Auto merge of #22040 - paulrouget:shutdown_canvas_paint_thread, r=jdm

Exit Canvas paint thread on shutdown

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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 #22038 (github issue number if applicable).

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components/canvas/canvas_paint_thread.rs

@@ -66,6 +66,7 @@ impl<'a> CanvasPaintThread <'a> {
                                     }
                                 }
                             },
+                            CanvasMsg::Exit => break,
                         }
                     },
                     Err(e) => {

components/canvas_traits/canvas.rs

@@ -27,6 +27,7 @@ pub enum CanvasMsg {
     FromScript(FromScriptMsg, CanvasId),
     Recreate(Size2D<u32>, CanvasId),
     Close(CanvasId),
+    Exit,
 }
 
 #[derive(Clone, Deserialize, Serialize)]

components/constellation/constellation.rs

@@ -1441,6 +1441,11 @@ where
             }
         }
 
+        debug!("Exiting Canvas Paint thread.");
+        if let Err(e) = self.canvas_chan.send(CanvasMsg::Exit) {
+            warn!("Exit Canvas Paint thread failed ({})", e);
+        }
+
         if let Some(webgl_threads) = self.webgl_threads.as_ref() {
             debug!("Exiting WebGL thread.");
             if let Err(e) = webgl_threads.exit() {