cros: Break BaseScreenHandler into two classes.

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

 // Copyright (c) 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_CHROMEOS_LOGIN_SCREENS_TERMS_OF_SERVICE_SCREEN_VIEW_H_
 #define CHROME_BROWSER_CHROMEOS_LOGIN_SCREENS_TERMS_OF_SERVICE_SCREEN_VIEW_H_
 
 #include <string>
+#include "chrome/browser/chromeos/login/oobe_screen.h"
 
 namespace chromeos {
 
 // Interface for dependency injection between TermsOfServiceScreen and its
 // WebUI representation.
 class TermsOfServiceScreenView {
  public:
   class Delegate {
    public:
     virtual ~Delegate() {}
 
     // Called when the user declines the Terms of Service.
     virtual void OnDecline() = 0;
 
     // Called when the user accepts the Terms of Service.
     virtual void OnAccept() = 0;
 
     // Called when view is destroyed so there is no dead reference to it.
     virtual void OnViewDestroyed(TermsOfServiceScreenView* view) = 0;
   };
 
+  constexpr static OobeScreen kScreenId = OobeScreen::SCREEN_TERMS_OF_SERVICE;
+
   virtual ~TermsOfServiceScreenView() {}
 
   // Sets screen this view belongs to.
   virtual void SetDelegate(Delegate* screen) = 0;
 
   // Shows the contents of the screen.
   virtual void Show() = 0;
 
   // Hides the contents of the screen.
   virtual void Hide() = 0;
 
   // Sets the domain name whose Terms of Service are being shown.
   virtual void SetDomain(const std::string& domain) = 0;
 
   // Called when the download of the Terms of Service fails. Show an error
   // message to the user.
   virtual void OnLoadError() = 0;
 
   // Called when the download of the Terms of Service is successful. Shows the
   // downloaded |terms_of_service| to the user.
   virtual void OnLoadSuccess(const std::string& terms_of_service) = 0;
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_SCREENS_TERMS_OF_SERVICE_SCREEN_VIEW_H_