cros: Break BaseScreenHandler into two classes.

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

Index: chrome/browser/chromeos/login/screens/user_image_view.h
diff --git a/chrome/browser/chromeos/login/screens/user_image_view.h b/chrome/browser/chromeos/login/screens/user_image_view.h
index d14ce6b13f4dcda0ad6fa8648141bd95e7fa7fbf..3464a1020549bec454ab58dc67b77a1a6deda636 100644
--- a/chrome/browser/chromeos/login/screens/user_image_view.h
+++ b/chrome/browser/chromeos/login/screens/user_image_view.h
@@ -5,6 +5,8 @@
 #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;
@@ -13,6 +15,8 @@ class UserImageScreen;
 // 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;