Add a subpage_id field to NewLayoutInfo.

src/components/main/pipeline.rs

@@ -88,6 +88,7 @@ impl Pipeline {
         let new_layout_info = NewLayoutInfo {
             old_pipeline_id: script_pipeline.id.clone(),
             new_pipeline_id: id,
+            subpage_id: subpage_id,
             layout_chan: layout_chan.clone(),
         };
 

src/components/script/script_task.rs

@@ -93,6 +93,7 @@ pub enum ScriptMsg {
 pub struct NewLayoutInfo {
     pub old_pipeline_id: PipelineId,
     pub new_pipeline_id: PipelineId,
+    pub subpage_id: SubpageId,
     pub layout_chan: LayoutChan,
 }
 
@@ -784,6 +785,7 @@ impl ScriptTask {
         let NewLayoutInfo {
             old_pipeline_id,
             new_pipeline_id,
+            subpage_id,
             layout_chan
         } = new_layout_info;