Show a spinner UI for zero-touch enrollment

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

 /* Copyright 2015 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. */
 
 #oauth-enrollment {
   height: 528px;
   padding: 0;
   width: 448px;
 }
 
 #oauth-enrollment.saml {
   padding-top: 44px;
   width: 562px;
 }
 
 #oauth-enroll-step-contents {
   color: #666;
   height: 100%;
   width: 100%;
 }
 
 #oauth-enroll-step-contents > div {
   display: none;
 }
 
+.oauth-enroll-state-working #oauth-enroll-step-working,
 .oauth-enroll-state-error #oauth-enroll-step-error,
 .oauth-enroll-state-success #oauth-enroll-step-success,
 .oauth-enroll-state-abe-success #oauth-enroll-step-abe-success {
   display: table;
   height: 480px;
   margin: 0 auto;
 }
 
-.oauth-enroll-state-working #oauth-enroll-step-signin,
 .oauth-enroll-state-attribute-prompt-error
     #oauth-enroll-step-attribute-prompt-error,
 .oauth-enroll-state-signin #oauth-enroll-step-signin,
 .oauth-enroll-state-attribute-prompt
     #oauth-enroll-step-attribute-prompt {
   display: block;
   height: 100%;
   width: 100%;
 }
 
@@ skipping 70 matching lines @@
 }
 
 .oauth-enroll-state-signin #oauth-enroll-navigation,
 .oauth-enroll-state-working #oauth-enroll-navigation {
   color: white;
 }
 
 #oauth-enrollment.saml #oauth-enroll-navigation {
   color: rgba(0, 0, 0, .54);
 }
-