MD Settings: avoid double pref observation on Startup Pages

chrome/browser/ui/webui/settings/chromeos/easy_unlock_settings_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_CHROMEOS_EASY_UNLOCK_SETTINGS_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_SETTINGS_CHROMEOS_EASY_UNLOCK_SETTINGS_HANDLER_H_
 
 #include "base/macros.h"
 #include "chrome/browser/signin/easy_unlock_service_observer.h"
-#include "content/public/browser/web_ui_message_handler.h"
+#include "chrome/browser/ui/webui/settings/md_settings_ui.h"
 
 namespace content {
 class WebUIDataSource;
 }
 
 class Profile;
 
 namespace chromeos {
 namespace settings {
 
-class EasyUnlockSettingsHandler : public content::WebUIMessageHandler,
+class EasyUnlockSettingsHandler : public ::settings::SettingsPageUIHandler,
                                   public EasyUnlockServiceObserver {
  public:
   // Returns nullptr if EasyUnlock is not allowed for this device.
   static EasyUnlockSettingsHandler* Create(
       content::WebUIDataSource* html_source,
       Profile* profile);
 
   ~EasyUnlockSettingsHandler() override;
 
-  // WebUIMessageHandler
+  // SettingsPageUIHandler:
   void RegisterMessages() override;
 
-  // EasyUnlockServiceObserver
+  // EasyUnlockServiceObserver:
   void OnTurnOffOperationStatusChanged() override;
 
  protected:
   explicit EasyUnlockSettingsHandler(Profile* profile);
 
  private:
   FRIEND_TEST_ALL_PREFIXES(EasyUnlockSettingsHandlerTest, TurnOffStatus);
 
   void SendTurnOffOperationStatus();
 
   // JS callbacks.
   void HandleGetTurnOffFlowStatus(const base::ListValue* args);
   void HandleRequestTurnOff(const base::ListValue* args);
   void HandlePageDismissed(const base::ListValue* args);
 
   Profile* const profile_;
 
   DISALLOW_COPY_AND_ASSIGN(EasyUnlockSettingsHandler);
 };
 
 }  // namespace settings
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_UI_WEBUI_SETTINGS_CHROMEOS_EASY_UNLOCK_SETTINGS_HANDLER_H_