[MD Settings][People] Disables profile name field for legacy supervised users.

chrome/browser/resources/settings/people_page/people_page.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.
 
 /**
  * @fileoverview
  * 'settings-people-page' is the settings page containing sign-in settings.
  */
 Polymer({
   is: 'settings-people-page',
@@ skipping 346 matching lines @@
    */
   getIconImageset_: function(iconUrl) {
     return cr.icon.getImage(iconUrl);
   },
 
   /**
    * @return {boolean} Whether to show the "Sign in to Chrome" button.
    * @private
    */
   showSignin_: function(syncStatus) {
-    return syncStatus.signinAllowed && !syncStatus.signedIn;
+    return !!syncStatus.signinAllowed && !syncStatus.signedIn;
   },
 });