cros: Show dircryto migration banner

ui/login/account_picker/screen_account_picker.js

 // 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.
 
 /**
  * @fileoverview Account picker screen implementation.
  */
 
 login.createScreen('AccountPickerScreen', 'account-picker', function() {
   /**
@@ skipping 370 matching lines @@
      * @param {string} user name.
      */
     removeUser: function(username) {
       $('pod-row').removeUserPod(username);
     },
 
     /**
      * Displays a banner containing |message|. If the banner is already present
      * this function updates the message in the banner. This function is used
      * by the chrome.screenlockPrivate.showMessage API.
-     * @param {string} message Text to be displayed
+     * @param {string} message Text to be displayed or empty to hide the banner.
      */
     showBannerMessage: function(message) {
       var banner = $('signin-banner');
       banner.textContent = message;
-      banner.classList.toggle('message-set', true);
+      banner.classList.toggle('message-set', !!message);
     },
 
     /**
      * Shows a custom icon in the user pod of |username|. This function
      * is used by the chrome.screenlockPrivate API.
      * @param {string} username Username of pod to add button
      * @param {!{id: !string,
      *           hardlockOnClick: boolean,
      *           isTrialRun: boolean,
      *           tooltip: ({text: string, autoshow: boolean} | undefined)}} icon
@@ skipping 89 matching lines @@
      * @param {string} userID The user ID of the public session
      * @param {string} locale The locale to which this list of keyboard layouts
      *     applies
      * @param {!Object} list List of available keyboard layouts
      */
     setPublicSessionKeyboardLayouts: function(userID, locale, list) {
       $('pod-row').setPublicSessionKeyboardLayouts(userID, locale, list);
     }
   };
 });