cros: Break BaseScreenHandler into two classes.

chrome/browser/chromeos/login/screens/user_image_view.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_USER_IMAGE_VIEW_H_
 #define CHROME_BROWSER_CHROMEOS_LOGIN_SCREENS_USER_IMAGE_VIEW_H_
 
+#include "chrome/browser/chromeos/login/oobe_screen.h"
+
 namespace chromeos {
 
 class UserImageScreen;
 
 // Interface for dependency injection between UserImageScreen and its actual
 // representation, either views based or WebUI.
 class UserImageView {
  public:
+  constexpr static OobeScreen kScreenId = OobeScreen::SCREEN_USER_IMAGE_PICKER;
+
   virtual ~UserImageView() {}
 
   virtual void Bind(UserImageScreen* screen) = 0;
 
   virtual void Unbind() = 0;
 
   // Shows the contents of the screen.
   virtual void Show() = 0;
 
   // Hides the contents of the screen.
   virtual void Hide() = 0;
 
   // Hides curtain with spinner.
   virtual void HideCurtain() = 0;
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_SCREENS_USER_IMAGE_VIEW_H_