AppListModel / AppsGridView: Better error handling for corner cases.

ui/app_list/views/apps_grid_view.cc

Index: ui/app_list/views/apps_grid_view.cc
diff --git a/ui/app_list/views/apps_grid_view.cc b/ui/app_list/views/apps_grid_view.cc
index 8d7db8e3059e040100923b4074cba36feee749ed..71911dbc2ca2905216fe8c023bc88cc9967064ce 100644
--- a/ui/app_list/views/apps_grid_view.cc
+++ b/ui/app_list/views/apps_grid_view.cc
@@ -1733,7 +1733,13 @@ void AppsGridView::MoveItemToFolder(AppListItemView* item_view,
                                     const Index& target) {
   const std::string& source_item_id = item_view->item()->id();
   AppListItemView* target_view = GetViewAtSlotOnCurrentPage(target.slot);
-  const std::string&  target_view_item_id = target_view->item()->id();
+  DCHECK(target_view);
+  const std::string& target_view_item_id = target_view->item()->id();
+
+  // Check that the item is not being dropped onto itself; this should not
+  // happen, but it can if something allows multiple views to share an
+  // item.

[calamity, 2014/09/26 03:55:18]

(e.g a folder drop does not clean up properly)

[Matt Giuca, 2014/09/29 03:05:03]

Done.

+  DCHECK_NE(source_item_id, target_view_item_id);
 
   // Make change to data model.
   item_list_->RemoveObserver(this);