Reland r221579: Files.app: Let the PreviewPanel class control the visibility of the preview panel.

chrome/browser/resources/file_manager/main.html

Index: chrome/browser/resources/file_manager/main.html
diff --git a/chrome/browser/resources/file_manager/main.html b/chrome/browser/resources/file_manager/main.html
index 1874116fe1b789b102114a4189fa113e4e802d37..abbd8d57312f23074d6d97972bb54d4d0329df9d 100644
--- a/chrome/browser/resources/file_manager/main.html
+++ b/chrome/browser/resources/file_manager/main.html
@@ -114,6 +114,7 @@
       <script src="js/suggest_apps_dialog.js"></script>
       <script src="js/text_measure.js"></script>
       <script src="js/tree.css.js"></script>
+      <script src="js/ui/preview_panel.js"></script>
       <script src="js/url_constants.js"></script>
       <script src="js/volume_manager.js"></script>
       <script src="js/media/media_util.js"></script>