Call preventDefault in all on-tap events that show a dialog.

chrome/browser/resources/settings/on_startup_page/startup_urls_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-startup-urls-page' is the settings page
  * containing the urls that will be opened when chrome is started.
  */
 
 Polymer({
@@ skipping 33 matching lines @@
     }.bind(this));
     this.browserProxy_.loadStartupPages();
 
     this.addEventListener(settings.EDIT_STARTUP_URL_EVENT, function(event) {
       this.startupUrlDialogModel_ = event.detail;
       this.showStartupUrlDialog_ = true;
       event.stopPropagation();
     }.bind(this));
   },
 
-  /** @private */
-  onAddPageTap_: function() {
+  /**
+   * @param {!Event} e
+   * @private
+   */
+  onAddPageTap_: function(e) {
+    e.preventDefault();
     this.showStartupUrlDialog_ = true;
   },
 
   /** @private */
   destroyUrlDialog_: function() {
     this.showStartupUrlDialog_ = false;
     this.startupUrlDialogModel_ = null;
   },
 
   /** @private */
   onUseCurrentPagesTap_: function() {
     this.browserProxy_.useCurrentPages();
   },
 });