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

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

 // Copyright (c) 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.
 
 #ifndef CHROME_BROWSER_UI_WEBUI_SETTINGS_MD_SETTINGS_UI_H_
 #define CHROME_BROWSER_UI_WEBUI_SETTINGS_MD_SETTINGS_UI_H_
 
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/values.h"
 #include "content/public/browser/web_ui_controller.h"
 #include "content/public/browser/web_ui_message_handler.h"
 
 namespace settings {
 
 // The base class handler of Javascript messages of settings pages.
 class SettingsPageUIHandler : public content::WebUIMessageHandler {
  public:
   SettingsPageUIHandler();
   ~SettingsPageUIHandler() override;
 
   // WebUIMessageHandler implementation.
   void RegisterMessages() override {}
 
+ protected:
+  // Helper method for responding to JS requests initiated with
+  // cr.sendWithPromise().
+  void CallJavascriptCallback(const base::Value& callback_id,
+                              const base::Value& response);
+
  private:
   DISALLOW_COPY_AND_ASSIGN(SettingsPageUIHandler);
 };
 
 // The WebUI handler for chrome://md-settings.
 class MdSettingsUI : public content::WebUIController {
  public:
   explicit MdSettingsUI(content::WebUI* web_ui);
   ~MdSettingsUI() override;
 
  private:
   void AddSettingsPageUIHandler(content::WebUIMessageHandler* handler);
 
   DISALLOW_COPY_AND_ASSIGN(MdSettingsUI);
 };
 
 }  // namespace settings
 
 #endif  // CHROME_BROWSER_UI_WEBUI_SETTINGS_MD_SETTINGS_UI_H_