chrome: Cleanup class/struct forward declarations

chrome/browser/ui/webui/flags_ui.h

 // Copyright (c) 2012 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_FLAGS_UI_H_
 #define CHROME_BROWSER_UI_WEBUI_FLAGS_UI_H_
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "build/build_config.h"
 #include "content/public/browser/web_ui_controller.h"
 #include "ui/base/layout.h"
 
 #if defined(OS_CHROMEOS)
 #include "chrome/browser/chromeos/settings/device_settings_service.h"
 #endif
 
-class PrefRegistrySimple;
-class Profile;
-
 namespace base {
 class RefCountedMemory;
 }
 
-namespace user_prefs {
-class PrefRegistrySyncable;
-}
-
 class FlagsUI : public content::WebUIController {
  public:
   explicit FlagsUI(content::WebUI* web_ui);
   ~FlagsUI() override;
 
   static base::RefCountedMemory* GetFaviconResourceBytes(
       ui::ScaleFactor scale_factor);
 
  private:
   base::WeakPtrFactory<FlagsUI> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(FlagsUI);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_FLAGS_UI_H_