Site Settings Desktop: Change how adding site exceptions work.

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({
   is: 'add-site-dialog',
 
   behaviors: [SiteSettingsBehavior],
 
   properties: {
     /**
      * The site to add an exception for.
      * @private
      */
     site_: String,
+
+    /**
+     * Whether this is an allow exception this dialog is adding.
+     */
+     allowException: Boolean,
   },
 
-  /** Opens the dialog. */
-  open: function() {
+  /**
+   * Opens the dialog.
+   * @param {string} type Whether this was launched from an Allow list or a
+   *     Block list.
+   */
+  open: function(type) {
+    this.allowException = type == settings.PermissionValues.ALLOW;
     this.$.dialog.open();
   },
 
   /**
    * 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));
   },
 
   /**
    * The tap handler for the Add [Site] button (adds the pattern and closes
    * the dialog).
    * @private
    */
-  onAddTap_: function() {
+  onSubmit_: function() {
+    if (this.$.add.disabled)
+      return;  // Can happen when Enter is pressed.
     var pattern = this.addPatternWildcard_(this.site_);
     this.setCategoryPermissionForOrigin(
-        pattern, '', this.category, settings.PermissionValues.ALLOW);
+        pattern, '', this.category, this.allowException ?
+            settings.PermissionValues.ALLOW : settings.PermissionValues.BLOCK);
     this.$.dialog.close();
   },
 });