MD Settings: Fix canceling of "Add site exception" dialog.

chrome/browser/resources/settings/site_settings/add_site_dialog.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.
 
 /**
  * @fileoverview
  * 'add-site-dialog' provides a dialog to add exceptions for a given Content
  * Settings category.
  */
 Polymer({
@@ skipping 28 matching lines @@
    * Validates that the pattern entered is valid.
    * @private
    */
   validate_: function() {
     var pattern = this.addPatternWildcard_(this.site_);
     this.browserProxy.isPatternValid(pattern).then(function(isValid) {
       this.$.add.disabled = !isValid;
     }.bind(this));
   },
 
+  /** @private */
+  onCancelTap_: function() {
+    this.$.dialog.cancel();
+  },
+
   /**
    * The tap handler for the Add [Site] button (adds the pattern and closes
    * the dialog).
    * @private
    */
   onSubmit_: function() {
     if (this.$.add.disabled)
       return;  // Can happen when Enter is pressed.
     var pattern = this.addPatternWildcard_(this.site_);
     this.setCategoryPermissionForOrigin(
         pattern, '', this.category, this.allowException ?
             settings.PermissionValues.ALLOW : settings.PermissionValues.BLOCK);
     this.$.dialog.close();
   },
 });