MD Settings: Add helper method for responding to cr.sendWithPromise.

chrome/browser/resources/settings/appearance_page/appearance_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.
 
 /**
  * 'settings-appearance-page' is the settings page containing appearance
  * settings.
  *
  * Example:
  *
@@ skipping 106 matching lines @@
     this.$.pageZoom.menuOptions = this.pageZoomOptions_;
     // TODO(dschuyler): Look into adding a listener for the
     // default zoom percent.
     chrome.settingsPrivate.getDefaultZoomPercent(
         this.zoomPrefChanged_.bind(this));
   },
 
   /** @override */
   attached: function() {
     // Query the initial state.
-    cr.sendWithPromise('getResetThemeEnabled').then(function(response) {
-      this.setResetThemeEnabled(response[0]);
-    }.bind(this));
+    cr.sendWithPromise('getResetThemeEnabled').then(
+        this.setResetThemeEnabled.bind(this));
 
     // Set up the change event listener.
     cr.addWebUIListener('reset-theme-enabled-changed',
                         this.setResetThemeEnabled.bind(this));
   },
 
   /**
    * @param {boolean} enabled Whether the theme reset is available.
    */
   setResetThemeEnabled: function(enabled) {
@@ skipping 32 matching lines @@
    * @param {number} percent The integer percentage of the page zoom.
    * @private
    */
   zoomLevelChanged_: function(percent) {
     // The |percent| may be undefined on startup.
     if (percent === undefined)
       return;
     chrome.settingsPrivate.setDefaultZoomPercent(percent);
   },
 });