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..1fb17f4bed2f35172c89e9f1cc847a88fe911285 100644
--- a/ui/app_list/app_list_model_observer.h
+++ b/ui/app_list/app_list_model_observer.h
@@ -30,6 +30,9 @@ class APP_LIST_EXPORT AppListModelObserver {
   // Triggered just after an item is deleted from the model.
   virtual void OnAppListItemDeleted() {}
 
+  // Triggered just after an item is uninstalled & deleted to clean up parent.

[jennyz, 2015/03/17 21:16:48]

parent -> |parent|.

[Greg Levin, 2015/03/23 22:04:50]

Since arg is now parent_id, I'm going to go with "folder" instead of a variable
name.

+  virtual void OnAppListChildItemUninstalled(AppListFolderItem* parent) {}

[stevenjb, 2015/03/23 19:34:30]

This is actually problematic. Currently we only handle
OnAppListChildItemUninstalled in AppListMainView, but that may end up deleting
the folder (|parent|), invalidating the pointer. So if anything else observes
this and handles it (or if there are ever multiple views associated with the
model), this could cause a crash.

We should pass the folder_id here instead.

[Greg Levin, 2015/03/23 22:04:50]

Done.

+
   // Triggered after |item| has moved, changed folders, or changed properties.
   virtual void OnAppListItemUpdated(AppListItem* item) {}