Fix null deref when hiding the PIN keyboard.

ui/login/account_picker/screen_account_picker.js

Index: ui/login/account_picker/screen_account_picker.js
diff --git a/ui/login/account_picker/screen_account_picker.js b/ui/login/account_picker/screen_account_picker.js
index 14652466d3eac6f0002b34d7a67d66b8b1aacddf..198888fab8786fbf496e4d6769d9fedd55c0519a 100644
--- a/ui/login/account_picker/screen_account_picker.js
+++ b/ui/login/account_picker/screen_account_picker.js
@@ -359,16 +359,7 @@ login.createScreen('AccountPickerScreen', 'account-picker', function() {
      * @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);
     },
 
     /**