[WebUI] Fix chrome://plugins regression by changing template class name.

chrome/browser/resources/plugins.css

 /* Copyright (c) 2012 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file. */
 
 body {
   margin: 10px;
   min-width: 47em;
 }
 
 a {
@@ skipping 213 matching lines @@
   -webkit-padding-start: 1em;
 }
 
 /* Make the MIME Types tables smaller. */
 .plugin-details .mime-types {
   font-size: 95%;
 }
 
 /* Separate the header from the contents in each MIME Types table. */
 .plugin-details .mime-types .header td {
-  /* border-bottom: 1px solid; */
+  border-bottom: 1px solid black;
   padding-bottom: 0.1em;
 }
 
 /* Separate the columns for tables used for horizontal listings only a bit. */
 .hlisting td+td {
   -webkit-padding-start: 0.4em;
 }
 
 /* Match the indentation of .plugin-text. */
 .plugin-actions {
   -webkit-padding-start: 5px;
   margin-bottom: 0.2em;
   margin-top: 0.2em;
 }
 
 .always-allow {
   -webkit-margin-start: 30px;
 }
 
 button {
   font-size: 104%;
 }