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

chrome/browser/resources/settings/languages_page/languages_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-languages-page' is the settings page
  * for language and input method settings.
  */
 (function() {
 'use strict';
@@ skipping 50 matching lines @@
   },
 
   /** @private */
   onBackTap_: function() {
     this.$.pages.back();
   },
 
   /**
    * Stamps and opens the Add Languages dialog, registering a listener to
    * disable the dialog's dom-if again on close.
+   * @param {!Event} e
    * @private
    */
-  onAddLanguagesTap_: function() {
+  onAddLanguagesTap_: function(e) {
+    e.preventDefault();
     this.showAddLanguagesDialog_ = true;
     this.async(function() {
       var dialog = this.$$('settings-add-languages-dialog');
       dialog.addEventListener('close', function() {
         this.showAddLanguagesDialog_ = false;
       }.bind(this));
     });
   },
 
   /**
@@ skipping 427 matching lines @@
     if (e.target.tagName == expandButtonTag)
       return;
 
     /** @type {!CrExpandButtonElement} */
     var expandButton = e.currentTarget.querySelector(expandButtonTag);
     assert(expandButton);
     expandButton.expanded = !expandButton.expanded;
   },
 });
 })();