After uninstall, remove last item in Launcher folder

ui/app_list/app_list_model_observer.h

Index: ui/app_list/app_list_model_observer.h
diff --git a/ui/app_list/app_list_model_observer.h b/ui/app_list/app_list_model_observer.h
index 09cccc0e75531c8daf4925962e3677f114af5a5b..7ed0af89b234258eade45ee3a5363a151a579110 100644
--- a/ui/app_list/app_list_model_observer.h
+++ b/ui/app_list/app_list_model_observer.h
@@ -30,6 +30,10 @@ class APP_LIST_EXPORT AppListModelObserver {
   // Triggered just after an item is deleted from the model.
   virtual void OnAppListItemDeleted() {}
 
+  // Triggered after uninstall of 2nd-to-last item in folder, before reparent of
+  // remaining item and folder removal.
+  virtual void OnSingleItemFolderWillBeDeleted(const std::string& folder_id) {}
+
   // Triggered after |item| has moved, changed folders, or changed properties.
   virtual void OnAppListItemUpdated(AppListItem* item) {}