Added back button when in folder view.

ui/app_list/views/contents_view.h

Index: ui/app_list/views/contents_view.h
diff --git a/ui/app_list/views/contents_view.h b/ui/app_list/views/contents_view.h
index a27300fe26be18311ed68ef5ff5d99c992357409..877b0b453ba464a0a3dc171acc95a6be371f368f 100644
--- a/ui/app_list/views/contents_view.h
+++ b/ui/app_list/views/contents_view.h
@@ -204,6 +204,9 @@ class APP_LIST_EXPORT ContentsView : public views::View,
   // The page that was showing before ShowSearchResults(true) was invoked.
   int page_before_search_;
 
+  // Whether the fullscreen app list feature is active.
+  const bool is_fullscreen_app_list_enabled_;
+
   // Manages the pagination for the launcher pages.
   PaginationModel pagination_model_;