Hide "Add user" button when enrollment screen is active.

chrome/browser/resources/chromeos/login/oobe_screen_oauth_enrollment_webview.js

 // 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.
 
 login.createScreen('OAuthEnrollmentScreen', 'oauth-enrollment', function() {
   /** @const */ var STEP_SIGNIN = 'signin';
   /** @const */ var STEP_WORKING = 'working';
   /** @const */ var STEP_ATTRIBUTE_PROMPT = 'attribute-prompt';
   /** @const */ var STEP_ERROR = 'error';
   /** @const */ var STEP_SUCCESS = 'success';
@@ skipping 159 matching lines @@
 
       return buttons;
     },
 
     /**
      * Event handler that is invoked just before the frame is shown.
      * @param {Object} data Screen init payload, contains the signin frame
      * URL.
      */
     onBeforeShow: function(data) {
+      $('login-header-bar').signinUIState = SIGNIN_UI_STATE.ENROLLMENT;
       var gaiaParams = {};
       gaiaParams.gaiaUrl = data.gaiaUrl;
       gaiaParams.gaiaPath = 'embedded/setup/chromeos';
       gaiaParams.isNewGaiaFlowChromeOS = true;
       gaiaParams.needPassword = false;
       if (data.management_domain) {
         gaiaParams.enterpriseDomain = data.management_domain;
         gaiaParams.emailDomain = data.management_domain;
       }
       gaiaParams.flow = 'enterprise';
       this.authenticator_.load(cr.login.Authenticator.AuthMode.DEFAULT,
                                gaiaParams);
 
       var modes = ['manual', 'forced', 'recovery'];
       for (var i = 0; i < modes.length; ++i) {
         this.classList.toggle('mode-' + modes[i],
                               data.enrollment_mode == modes[i]);
       }
       this.isCancelDisabled = true;
       this.showStep(STEP_SIGNIN);
     },
 
+    onBeforeHide: function() {
+      $('login-header-bar').signinUIState = SIGNIN_UI_STATE.HIDDEN;
+    },
+
     /**
      * Shows attribute-prompt step with pre-filled asset ID and
      * location.
      */
     showAttributePromptStep: function(annotated_asset_id, annotated_location) {
       $('oauth-enroll-asset-id').value = annotated_asset_id;
       $('oauth-enroll-location').value = annotated_location;
       $('oauth-enroll-back-button').hidden = true;
 
       this.showStep(STEP_ATTRIBUTE_PROMPT);
@@ skipping 72 matching lines @@
      * Uploads the device attributes to server. This goes to C++ side through
      * |chrome| and launches the device attribute update negotiation.
      */
     onAttributesSubmitted: function() {
       chrome.send('oauthEnrollAttributes',
                   [$('oauth-enroll-asset-id').value,
                    $('oauth-enroll-location').value]);
     }
   };
 });