After uninstall, remove last item in Launcher folder

ui/app_list/views/app_list_main_view.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/app_list/views/app_list_main_view.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/callback.h"
@@ skipping 248 matching lines @@
     // Animate to the start page if currently on the custom page view. The view
     // will hide on animation completion.
     contents_view_->SetActivePage(
         contents_view_->GetPageIndexForState(AppListModel::STATE_START));
   } else {
     // Hide the view immediately otherwise.
     contents_view_->custom_page_view()->SetVisible(false);
   }
 }
 
+// If |folder_id| is open, this will remove AppItemList from the folder's
+// AppsGridView before the folder is deleted.
+void AppListMainView::OnSingleItemFolderWillBeDeleted(
+    const std::string& folder_id) {
+  AppListFolderView* folder_view =
+      contents_view_->apps_container_view()->app_list_folder_view();
+  AppListFolderItem* open_folder_item = folder_view->folder_item();
+
+  if (open_folder_item && open_folder_item->id() == folder_id &&
+      contents_view_->apps_container_view()->IsInFolderView()) {
+    AppsGridView* folder_grid_view = folder_view->items_grid_view();
+    if (folder_grid_view)
+      folder_grid_view->SetItemList(nullptr);  // removes observer
+  }
+}
+
 void AppListMainView::OnCustomLauncherPageEnabledStateChanged(bool enabled) {
   views::View* custom_page = contents_view_->custom_page_view();
   if (!custom_page)
     return;
 
   if (ShouldShowCustomLauncherPage()) {
     // Make the custom page view visible again.
     custom_page->SetVisible(true);
   } else if (contents_view_->IsStateActive(
                  AppListModel::STATE_CUSTOM_LAUNCHER_PAGE)) {
@@ skipping 56 matching lines @@
     contents_view_->search_results_page_view()->SetSelection(select);
 }
 
 void AppListMainView::OnResultInstalled(SearchResult* result) {
   // Clears the search to show the apps grid. The last installed app
   // should be highlighted and made visible already.
   search_box_view_->ClearSearch();
 }
 
 }  // namespace app_list