CrOS files app: Stop using <paper-dialog>, use plain <dialog> instead.

ui/file_manager/file_manager/foreground/elements/files_quick_view.css

Index: ui/file_manager/file_manager/foreground/elements/files_quick_view.css
diff --git a/ui/file_manager/file_manager/foreground/elements/files_quick_view.css b/ui/file_manager/file_manager/foreground/elements/files_quick_view.css
index 60610bb3774d100291b815a65bff7a58b5fdbcc7..a2e19dac24c1e574bad7d4e20ec659f38f96ce10 100644
--- a/ui/file_manager/file_manager/foreground/elements/files_quick_view.css
+++ b/ui/file_manager/file_manager/foreground/elements/files_quick_view.css
@@ -7,14 +7,25 @@
   padding: 0;
 }
 
-paper-dialog {
+dialog {
   background-color: transparent;
-  /* Overrides paper-dialog's default font size. */
+  border: none;
   font-size: 100%;
   height: 100%;
   margin: 0;
   padding: 0;
   width: 100%;
+  opacity: 0;
+}
+
+dialog[open] {
+  opacity: 1;
+  transition: opacity 0.2s;
+}
+
+dialog::backdrop {
+  background-color: #000;
+  opacity: 0.6;
 }
 
 .thumbnail {