Use classList#toggle instead of classList[whatever ? 'add' : 'remove'].

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

 // Copyright (c) 2012 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.
  */
 
 cr.define('login', function() {
   /**
@@ skipping 157 matching lines @@
    */
   AccountPickerScreen.updateUserGaiaNeeded = function(username) {
     $('pod-row').resetUserOAuthTokenStatus(username);
   };
 
   /**
    * Updates Caps Lock state (for Caps Lock hint in password input field).
    * @param {boolean} enabled Whether Caps Lock is on.
    */
   AccountPickerScreen.setCapsLockState = function(enabled) {
-    $('pod-row').classList[enabled ? 'add' : 'remove']('capslock-on');
+    $('pod-row').classList.toggle('capslock-on', enabled);
   };
 
   /**
    * Enforces focus on user pod of locked user.
    */
   AccountPickerScreen.forceLockedUserPodFocus = function() {
     var row = $('pod-row');
     if (row.lockedPod)
       row.focusPod(row.lockedPod, true);
   };
 
   return {
     AccountPickerScreen: AccountPickerScreen
   };
 });