cros: Remove usage of GaiaScreenHandler outside of login/webui.

chrome/browser/chromeos/login/screens/gaia_screen.h

 // Copyright 2014 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_CHROMEOS_LOGIN_SCREENS_GAIA_SCREEN_H_
 #define CHROME_BROWSER_CHROMEOS_LOGIN_SCREENS_GAIA_SCREEN_H_
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 
 namespace chromeos {
 
-class LoginDisplayWebUIHandler;
-class GaiaScreenHandler;
+class GaiaView;
 
 // This class represents GAIA screen: login screen that is responsible for
 // GAIA-based sign-in.
 class GaiaScreen {
  public:
-  GaiaScreen();
-  virtual ~GaiaScreen();
-  void SetLegacyHandler(LoginDisplayWebUIHandler* handler);
-  void SetScreenHandler(GaiaScreenHandler* handler);
+  GaiaScreen() = default;
+  virtual ~GaiaScreen() = default;
+
+  void set_view(GaiaView* view) { view_ = view; }
+
   void MaybePreloadAuthExtension();
 
  private:
-  LoginDisplayWebUIHandler* legacy_handler_;
-  GaiaScreenHandler* screen_handler_;
+  GaiaView* view_ = nullptr;
 
   DISALLOW_COPY_AND_ASSIGN(GaiaScreen);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_SCREENS_GAIA_SCREEN_H_