MD Settings: Fix Appearance home page URL crash

chrome/browser/ui/webui/settings/on_startup_handler.h

 // 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.
 
 #ifndef CHROME_BROWSER_UI_WEBUI_SETTINGS_ON_STARTUP_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_SETTINGS_ON_STARTUP_HANDLER_H_
 
 #include "base/macros.h"
 #include "chrome/browser/ui/webui/settings/settings_page_ui_handler.h"
 
@@ skipping 10 matching lines @@
 
   // SettingsPageUIHandler:
   void RegisterMessages() override;
   void OnJavascriptAllowed() override {}
   void OnJavascriptDisallowed() override {}
 
  private:
   // Handler for the "getNtpExtension" message. No arguments.
   void HandleGetNtpExtension(const base::ListValue* /*args*/);
 
+  // Handles the "validateStartupPage" message. Passed a URL that might be a
+  // valid startup page.
+  void HandleValidateStartupPage(const base::ListValue* args);
+
   DISALLOW_COPY_AND_ASSIGN(OnStartupHandler);
 };
 
 }  // namespace settings
 
 #endif  // CHROME_BROWSER_UI_WEBUI_SETTINGS_ON_STARTUP_HANDLER_H_