Make the layout content process shutdown sender optional.

components/constellation/pipeline.rs

@@ -166,7 +166,7 @@ impl Pipeline {
                     window_size: window_size,
                     pipeline_port: pipeline_port,
                     layout_to_constellation_chan: state.layout_to_constellation_chan.clone(),
-                    content_process_shutdown_chan: layout_content_process_shutdown_chan.clone(),
+                    content_process_shutdown_chan: Some(layout_content_process_shutdown_chan.clone()),
                     layout_threads: PREFS.get("layout.threads").as_u64().expect("count") as usize,
                 };
 
@@ -448,7 +448,7 @@ impl UnprivilegedPipelineContent {
                     self.font_cache_thread,
                     self.time_profiler_chan,
                     self.mem_profiler_chan,
-                    self.layout_content_process_shutdown_chan,
+                    Some(self.layout_content_process_shutdown_chan),
                     self.webrender_api_sender,
                     self.prefs.get("layout.threads").expect("exists").value()
                         .as_u64().expect("count") as usize);

components/layout_thread/lib.rs

@@ -246,7 +246,7 @@ impl LayoutThreadFactory for LayoutThread {
               font_cache_thread: FontCacheThread,
               time_profiler_chan: time::ProfilerChan,
               mem_profiler_chan: mem::ProfilerChan,
-              content_process_shutdown_chan: IpcSender<()>,
+              content_process_shutdown_chan: Option<IpcSender<()>>,
               webrender_api_sender: webrender_traits::RenderApiSender,
               layout_threads: usize) {
         thread::spawn_named(format!("LayoutThread {:?}", id),
@@ -278,7 +278,9 @@ impl LayoutThreadFactory for LayoutThread {
                     layout.start();
                 }, reporter_name, sender, Msg::CollectReports);
             }
-            let _ = content_process_shutdown_chan.send(());
+            if let Some(content_process_shutdown_chan) = content_process_shutdown_chan {
+                let _ = content_process_shutdown_chan.send(());
+            }
         });
     }
 }

components/layout_traits/lib.rs

@@ -44,7 +44,7 @@ pub trait LayoutThreadFactory {
               font_cache_thread: FontCacheThread,
               time_profiler_chan: time::ProfilerChan,
               mem_profiler_chan: mem::ProfilerChan,
-              content_process_shutdown_chan: IpcSender<()>,
+              content_process_shutdown_chan: Option<IpcSender<()>>,
               webrender_api_sender: webrender_traits::RenderApiSender,
               layout_threads: usize);
 }

components/script_layout_interface/message.rs

@@ -142,6 +142,6 @@ pub struct NewLayoutThreadInfo {
     pub constellation_chan: IpcSender<ConstellationMsg>,
     pub script_chan: IpcSender<ConstellationControlMsg>,
     pub image_cache_thread: ImageCacheThread,
-    pub content_process_shutdown_chan: IpcSender<()>,
+    pub content_process_shutdown_chan: Option<IpcSender<()>>,
     pub layout_threads: usize,
 }

components/script_traits/lib.rs

@@ -180,7 +180,7 @@ pub struct NewLayoutInfo {
     /// A sender for the layout thread to communicate to the constellation.
     pub layout_to_constellation_chan: IpcSender<LayoutMsg>,
     /// A shutdown channel so that layout can tell the content process to shut down when it's done.
-    pub content_process_shutdown_chan: IpcSender<()>,
+    pub content_process_shutdown_chan: Option<IpcSender<()>>,
     /// Number of threads to use for layout.
     pub layout_threads: usize,
 }