Fix null deref when hiding the PIN keyboard.

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 341 matching lines @@
      */
     setTouchViewState: function(isTouchViewEnabled) {
       $('pod-row').setTouchViewState(isTouchViewEnabled);
     },
 
     /**
      * Hides the PIN keyboard if it's active.
      * @param {!user} user The user who can no longer enter a PIN.
      */
     disablePinKeyboardForUser: function(user) {
-      var pinContainer = $('pin-container');
-
-      // Transition opacity to 0, and when the transition is done hide the
-      // keyboard so it doesn't take layout space.
-      pinContainer.style.opacity = 0;
-      pinContainer.addEventListener('webkitTransitionEnd', function f(e) {
-        pinContainer.removeEventListener('webkitTransitionEnd', f);
-        pinContainer.hidden = true;
-      });
-      ensureTransitionEndEvent(pinContainer);
+      $('pod-row').setPinVisibility(user, false);
     },
 
     /**
      * Updates the display name shown on a public session pod.
      * @param {string} userID The user ID of the public session
      * @param {string} displayName The new display name
      */
     setPublicSessionDisplayName: function(userID, displayName) {
       $('pod-row').setPublicSessionDisplayName(userID, displayName);
     },
@@ skipping 21 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);
     }
   };
 });