Truncate long file name with ellipsis.

BUG=524114
TEST=manually

Review-Url: https://codereview.chromium.org/2027553006
Cr-Commit-Position: refs/heads/master@{#398263}

ui/file_manager/gallery/css/gallery.css

@@ -341,6 +341,7 @@ files-toggle-ripple::shadow .ripple.activated {
   margin: 8px 0;
   min-width: 160px;
   padding: 4px 0;
+  text-overflow: ellipsis;
   width: -webkit-fit-content;
 }