MD User Manager: Display error message when all profiles are locked.

chrome/browser/resources/md_user_manager/control_bar.js

 // Copyright 2016 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 'control-bar' is the horizontal bar at the bottom of the user
  * manager screen.
  */
  Polymer({
   is: 'control-bar',
 
+  behaviors: [
+    I18nBehavior,
+  ],
+
   properties: {
     /**
      * True if 'Browse as Guest' button is displayed.
      * @type {boolean}
      */
     showGuest: {
       type: Boolean,
       value: false
     },
 
@@ skipping 21 matching lines @@
    * @private
    */
   onLaunchGuestTap_: function(event) {
     this.browserProxy_.launchGuestUser();
   },
 
   /**
    * Handler for 'Add Person' button click event.
    * @param {!Event} event
    * @private
+   * @suppress {checkTypes}
    */
   onAddUserTap_: function(event) {
-    // Event is caught by user-manager-pages.
-    this.fire('change-page', {page: 'create-user-page'});
+    if (cr.ui.UserManager.getInstance().areAllProfilesLocked) {
+      cr.ui.UserManager.showErrorDialog(
+          this.i18n('AddProfileAllProfilesLockedError'));
+    } else {
+      // Event is caught by user-manager-pages.
+      this.fire('change-page', {page: 'create-user-page'});
+    }
   }
 });