Files app: Remove DOM attr/class when FilesNg is disabled

Bug: 1035691,992819,992821,992818
Change-Id: Ie560caf9f760e0baae734f7d9bcccdb9b73382df
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2087244
Auto-Submit: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Commit-Queue: Luciano Pacheco <lucmult@chromium.org>
Cr-Commit-Position: refs/heads/master@{#747123}

ui/file_manager/file_manager/foreground/js/file_manager.js

@@ -765,6 +765,8 @@ class FileManager extends cr.EventTarget {
     metrics.startInterval('Load.InitUI');
     if (util.isFilesNg()) {
       this.dialogDom_.classList.add('files-ng');
+    } else {
+      this.dialogDom_.classList.remove('files-ng');
     }
     this.initEssentialUI_();
     this.initAdditionalUI_();
@@ -895,6 +897,8 @@ class FileManager extends cr.EventTarget {
       // Move the dialog header to the side of the splitter above the list view.
       const dialogMain = queryRequiredElement('.dialog-main');
       dialogMain.insertBefore(dialogHeader, dialogMain.firstChild);
+    } else {
+      dialogHeader.classList.remove('files-ng');
     }
 
     // Create the root view of FileManager.

ui/file_manager/file_manager/foreground/js/ui/directory_tree.js

@@ -2459,6 +2459,8 @@ DirectoryTree.decorate =
         directorytree.styleRowElementDepth =
             directorytree.styleRowElementDepthFilesNG;
         el.setAttribute('files-ng', '');
+      } else {
+        el.removeAttribute('files-ng');
       }
 
       Object.freeze(directorytree);