For Mac, add AppListViewDelegateObserver::OnShutdown

ui/app_list/views/app_list_view.cc

Index: ui/app_list/views/app_list_view.cc
diff --git a/ui/app_list/views/app_list_view.cc b/ui/app_list/views/app_list_view.cc
index 4d7df429019d6108dd2b1772e6a3a7135557c3ec..2a01e8281fd04852f72a91028700fa5f324451b1 100644
--- a/ui/app_list/views/app_list_view.cc
+++ b/ui/app_list/views/app_list_view.cc
@@ -282,6 +282,11 @@ void AppListView::OnProfilesChanged() {
   app_list_main_view_->search_box_view()->InvalidateMenu();
 }
 
+void AppListView::OnShutdown() {
+  // Nothing to do on views - the widget will soon be closed, which will tear
+  // everything down.
+}
+
 void AppListView::SetProfileByPath(const base::FilePath& profile_path) {
   delegate_->SetProfileByPath(profile_path);
   app_list_main_view_->ModelChanged();