[quickview] Add a delete-confirm-dialog styling TODO

The <dialog> element added in CL:2033012 is too dark. We should restyle
its CSS ::backdrop property in quick-view.css to lighten it up

   dialog#delete-confirm-dialog::backdrop {
     ...
   }

Add TODO item for that task.

Tbr: alex
Bug: 803259
Change-Id: Id8f2408f6d9d6cc02f612e1794a52e54dcd2351d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2035493
Commit-Queue: Noel Gordon <noel@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#737994}

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

@@ -278,6 +278,7 @@ class QuickViewController {
 
     // Create a delete confirm dialog if needed.
     if (!this.deleteConfirmDialog_) {
+      // TODO(crbug.com/803259): style this element to make it lighter.
       const dialogElement = document.createElement('dialog');
       this.quickView_.shadowRoot.appendChild(dialogElement);
       dialogElement.id = 'delete-confirm-dialog';