Use webkit-margin-end for details element to get same margin for both ltr and rtl

Source/core/css/html.css

 /*
  * The default style sheet used to render HTML.
  *
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 1110 matching lines @@
 }
 
 summary {
     display: block
 }
 
 summary::-webkit-details-marker {
     display: inline-block;
     width: 0.66em;
     height: 0.66em;
-    margin-right: 0.4em;
+    -webkit-margin-end: 0.4em;
 }
 
 template {
     display: none
 }
 
 bdi, output {
     unicode-bidi: -webkit-isolate;
 }
 
@@ skipping 10 matching lines @@
 @page {
     /* FIXME: Define the right default values for page properties. */
     size: auto;
     margin: auto;
     padding: 0px;
     border-width: 0px;
 }
 
 /* noscript is handled internally, as it depends on settings. */