Do not make a subclass of Text only to disable selection.

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 664 matching lines @@
 
 input[type="radio"], input[type="checkbox"] {
     margin: 3px 0.5ex;
     padding: initial;
     background-color: initial;
     border: initial;
 }
 
 input[type="button"], input[type="submit"], input[type="reset"] {
     -webkit-appearance: push-button;
+    -webkit-user-select: none;
     white-space: pre
 }
 
 input[type="file"]::-webkit-file-upload-button {
     -webkit-appearance: push-button;
     -webkit-user-modify: read-only !important;
     white-space: nowrap;
     margin: 0;
     font-size: inherit;
 }
@@ skipping 428 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. */