Add a sign-in promo message to the Other Devices menu.

chrome/browser/resources/ntp4/footer_menu.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. */
 
 .footer-menu-button {
   -webkit-appearance: none;
   -webkit-padding-end: 15px;
   -webkit-padding-start: 9px;
   -webkit-transition: opacity 200ms;
   -webkit-transition-delay: 100ms;
@@ skipping 110 matching lines @@
 }
 
 .disclosure-triangle {
   -webkit-margin-start: 2px;
   -webkit-mask-image: url('images/disclosure_triangle_mask.png');
   background-color: #7F7F7F;
   display: inline-block;
   height: 9px;
   width: 9px;
 }
+
+.footer-menu .promo-message {
+  padding: 2px 4px;
+}
+
+.footer-menu p {
+  margin: 0;
+}