Remove persistent app list folders when they become empty

In crrev.com/c/1454156 the checks in
AppsGridView::ReparentItemForReorder and
AppsGridView::ReparentItemToAnotherFolder to see if a folder would be
deleted by removing an app was broken for persistent folders. This
would cause the model for the folder to be deleted, while the view
remained in place. Interacting with the empty folder would then cause
a null dereference and crash chrome.

Bug: 1009989
Change-Id: Ief7bc007683b38d536aabb1418d8142e5c0f7702
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1837556Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Fergus Dall <sidereal@google.com>
Cr-Commit-Position: refs/heads/master@{#702884}

ash/app_list/views/apps_grid_view.cc

@@ -2344,10 +2344,10 @@ void AppsGridView::ReparentItemForReorder(AppListItemView* item_view,
   int target_model_index = GetTargetModelIndexForMove(item_view, target);
   int target_item_index = GetTargetItemIndexForMove(item_view, target);
 
-  // If the folder is a candidate for removal, the view needs to be updated
-  // accordingly.
+  // Remove the source folder view if there is only 1 item in it, since the
+  // source folder will be deleted after its only child item removed from it.
   GridIndex target_override = target;
-  if (source_folder->ShouldAutoRemove()) {
+  if (source_folder->ChildItemCount() == 1u) {
     const int deleted_folder_index =
         view_model_.GetIndexOfView(activated_folder_item_view_);
     const GridIndex deleted_folder_grid_index =
@@ -2415,8 +2415,10 @@ bool AppsGridView::ReparentItemToAnotherFolder(AppListItemView* item_view,
   // Make change to data model.
   item_list_->RemoveObserver(this);
 
-  // Remove the source folder view if the folder is a candidate for removal.
-  if (source_folder->ShouldAutoRemove()) {
+  // Remove the source folder view if there is only 1 item in it, since the
+  // source folder will be deleted after its only child item merged into the
+  // target item.
+  if (source_folder->ChildItemCount() == 1u) {
     DeleteItemViewAtIndex(
         view_model_.GetIndexOfView(activated_folder_item_view()),
         false /* sanitize */);