report panic to embedder

components/compositing/compositor_thread.rs

@@ -146,6 +146,8 @@ pub enum EmbedderMsg {
     LoadStart(TopLevelBrowsingContextId),
     /// The load of a page has completed
     LoadComplete(TopLevelBrowsingContextId),
+    /// A pipeline panicked. First string is the reason, second one is the backtrace.
+    Panic(TopLevelBrowsingContextId, String, Option<String>),
 }
 
 /// Messages from the painting thread and the constellation thread to the compositor thread.
@@ -237,6 +239,7 @@ impl Debug for EmbedderMsg {
             EmbedderMsg::SetFullscreenState(..) => write!(f, "SetFullscreenState"),
             EmbedderMsg::LoadStart(..) => write!(f, "LoadStart"),
             EmbedderMsg::LoadComplete(..) => write!(f, "LoadComplete"),
+            EmbedderMsg::Panic(..) => write!(f, "Panic"),
         }
     }
 }

components/compositing/windowing.rs

@@ -189,4 +189,7 @@ pub trait WindowMethods {
     /// will want to avoid blocking on UI events, and just
     /// run the event loop at the vsync interval.
     fn set_animation_state(&self, _state: AnimationState) {}
+
+    /// Called when a pipeline panics.
+    fn handle_panic(&self, browser_id: TopLevelBrowsingContextId, reason: String, backtrace: Option<String>);
 }