md-settings: wrap lock screen dialogs in dom-if.

chrome/browser/resources/settings/people_page/fingerprint_list.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.
 
 (function() {
 'use strict';
 
 /**
  * The duration in ms of a background flash when a user touches the fingerprint
  * sensor on this page.
@@ skipping 13 matching lines @@
   properties: {
     /**
      * The list of fingerprint objects.
      * @private {!Array<string>}
      */
     fingerprints_: {
       type: Array,
       value: function() {
         return [];
       }
-    }
+    },
+
+    /** @private */
+    showSetupFingerprintDialog_: Boolean,
   },
 
   /** @private {?settings.FingerprintBrowserProxy} */
   browserProxy_: null,
 
   /** @override */
   attached: function() {
     this.addWebUIListener(
         'on-fingerprint-attempt-received', this.onAttemptReceived_.bind(this));
     this.addWebUIListener('on-screen-locked', this.onScreenLocked_.bind(this));
@@ skipping 93 matching lines @@
           if (success)
             this.updateFingerprintsList_();
         }.bind(this));
   },
 
   /**
    * Opens the setup fingerprint dialog.
    * @private
    */
   openAddFingerprintDialog_: function() {
-    this.$.setupFingerprint.open();
+    this.showSetupFingerprintDialog_ = true;
   },
 
   /** @private */
   onSetupFingerprintDialogClose_: function() {
+    this.showSetupFingerprintDialog_ = false;
     cr.ui.focusWithoutInk(assert(this.$$('#addFingerprint')));
     this.browserProxy_.startAuthentication();
   },
 
   /**
    * Close the setup fingerprint dialog when the screen is unlocked.
    * @param {boolean} screenIsLocked
    * @private
    */
   onScreenLocked_: function(screenIsLocked) {
     if (!screenIsLocked &&
         settings.getCurrentRoute() == settings.Route.FINGERPRINT) {
-      this.$.setupFingerprint.close();
+      this.onSetupFingerprintDialogClose_();
     }
   },
 });
 })();