Sync promo: Only show skip button on startup

chrome/browser/resources/sync_promo/sync_promo.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.
  */
 
 html {
   font-family: segoe ui, arial, helvetica, sans-serif;
   font-size: 13px;
 }
 
@@ skipping 41 matching lines @@
 /* Links and buttons. *********************************************************/
 
 #promo-skip-button,
 #promo-skip-button:hover,
 #promo-advanced,
 #promo-advanced:hover,
 #sync-setup-overlay * a:link {
   color: rgb(17, 85, 204);
 }
 
+html:not([isstartup]) #promo-skip-button {
+  display: none;
+}
+
 #sync-setup-overlay * a:visited {
   color: rgb(102, 17, 12);
 }
 
 #promo-skip-button:active,
 #promo-advanced:active,
 #sync-setup-overlay * a:active {
   color: rgb(209, 72, 54);
 }
 
@@ skipping 44 matching lines @@
 
 #promo-title-container h2 {
   color: rgb(102, 102, 102);
   font-size: 14px;
   font-weight: normal;
 }
 
 #promo-learn-more {
   display: inline-block;
 }