Add close button to the supervised user pages.

chrome/browser/resources/chromeos/login/screen_supervised_user_creation.css

 /* Copyright 2014 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.
  *
  * This is the stylesheet used by the Locally managed user creation flow screen.
  */
 
 #supervised-user-creation {
   height: 609px; /* Same size as GAIA sign in screen.*/
   padding: 0 0;  /* Some screens have elements right next to borders. */
@@ skipping 531 matching lines @@
   margin-left: -22px;
   margin-top: -22px;
   position: absolute;
   top: 50%;
   width: 44px;
 }
 
 .camera.live:not(.online) .supervised-user-creation-image-stream-area .spinner {
   display: block;
 }
+
+#supervised-user-creation-close-button-item {
+  color: rgba(0, 0, 0, .54);
+  position: absolute;
+  right: 10px;
+  top: 10px;
+  z-index: 1;
+}
+
+html[dir=rtl] #supervised-user-creation-close-button-item {
+  left: 10px;
+  right: auto;
+}