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

chrome/browser/resources/settings/site_settings/site_list.js

Index: chrome/browser/resources/settings/site_settings/site_list.js
diff --git a/chrome/browser/resources/settings/site_settings/site_list.js b/chrome/browser/resources/settings/site_settings/site_list.js
index d121b5bedbfc14756f56fe83496114658963596f..188cb67c13b40abb04953f160684c302ade108d2 100644
--- a/chrome/browser/resources/settings/site_settings/site_list.js
+++ b/chrome/browser/resources/settings/site_settings/site_list.js
@@ -217,9 +217,11 @@ Polymer({
 
   /**
    * A handler for the Add Site button.
+   * @param {!Event} e
    * @private
    */
-  onAddSiteTap_: function() {
+  onAddSiteTap_: function(e) {
+    e.preventDefault();
     var dialog = document.createElement('add-site-dialog');
     dialog.category = this.category;
     dialog.contentSetting = this.categorySubtype;