chrome: Cleanup class/struct forward declarations

chrome/browser/ui/webui/chromeos/login/user_board_screen_handler.h

 // Copyright 2013 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_CHROMEOS_LOGIN_USER_BOARD_SCREEN_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_CHROMEOS_LOGIN_USER_BOARD_SCREEN_HANDLER_H_
 
 #include <memory>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/values.h"
 #include "chrome/browser/chromeos/login/ui/views/user_board_view.h"
 #include "chrome/browser/ui/webui/chromeos/login/base_screen_handler.h"
 
 namespace chromeos {
 
-class SigninScreenHandler;
-
 // A class that handles WebUI hooks in Gaia screen.
 class UserBoardScreenHandler : public BaseScreenHandler, public UserBoardView {
  public:
   UserBoardScreenHandler();
   ~UserBoardScreenHandler() override;
 
  private:
   // BaseScreenHandler implementation:
   void DeclareLocalizedValues(
       ::login::LocalizedValuesBuilder* builder) override;
@@ skipping 28 matching lines @@
   void Unbind() override;
 
   UserBoardModel* model_;
 
   DISALLOW_COPY_AND_ASSIGN(UserBoardScreenHandler);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_UI_WEBUI_CHROMEOS_LOGIN_USER_BOARD_SCREEN_HANDLER_H_