MD Settings: validate home button url input

chrome/browser/resources/settings/appearance_page/appearance_browser_proxy.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.
 
 cr.define('settings', function() {
   /** @interface */
   function AppearanceBrowserProxy() {}
 
   AppearanceBrowserProxy.prototype = {
     /** @return {!Promise<number>} */
@@ skipping 10 matching lines @@
 
 // <if expr="chromeos">
     openWallpaperManager: assertNotReached,
 // </if>
 
     useDefaultTheme: assertNotReached,
 
 // <if expr="is_linux and not chromeos">
     useSystemTheme: assertNotReached,
 // </if>
+
+    /**
+     * @param {string} url The url of which to check validity.
+     * @return {!Promise<boolean>}
+     */
+    validateStartupPage: assertNotReached,
   };
 
   /**
    * @implements {settings.AppearanceBrowserProxy}
    * @constructor
    */
   function AppearanceBrowserProxyImpl() {}
 
   cr.addSingletonGetter(AppearanceBrowserProxyImpl);
 
@@ skipping 28 matching lines @@
     useDefaultTheme: function() {
       chrome.send('useDefaultTheme');
     },
 
 // <if expr="is_linux and not chromeos">
     /** @override */
     useSystemTheme: function() {
       chrome.send('useSystemTheme');
     },
 // </if>
+
+    /** @override */
+    validateStartupPage: function(url) {
+      return cr.sendWithPromise('validateStartupPage', url);
+    },
   };
 
   return {
     AppearanceBrowserProxy: AppearanceBrowserProxy,
     AppearanceBrowserProxyImpl: AppearanceBrowserProxyImpl,
   };
 });