Add tiles to the experimental app list start page.

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 ce72ee52b93f107b87c8f84bce9d3d2924027161..25275018a201dae2f4d3b4bbfeb9863ba661d8d9 100644
--- a/ui/app_list/app_list_model_observer.h
+++ b/ui/app_list/app_list_model_observer.h
@@ -22,6 +22,9 @@ class APP_LIST_EXPORT AppListModelObserver {
   // Triggered just before an item is deleted from the model.
   virtual void OnAppListItemWillBeDeleted(AppListItem* item) {}
 
+  // Triggered just after an item is deleted from the model.
+  virtual void OnAppListItemDeleted() {}
+
   // Triggered after |item| has moved, changed folders, or changed properties.
   virtual void OnAppListItemUpdated(AppListItem* item) {}