cros: Break BaseScreenHandler into two classes.

chrome/browser/chromeos/login/enrollment/enrollment_screen_view.h

Index: chrome/browser/chromeos/login/enrollment/enrollment_screen_view.h
diff --git a/chrome/browser/chromeos/login/enrollment/enrollment_screen_view.h b/chrome/browser/chromeos/login/enrollment/enrollment_screen_view.h
index 9b438498467c53d2f27522673ea4874595af0cef..cebbbc342b54ae7ae97602a444b2a40c77cf7370 100644
--- a/chrome/browser/chromeos/login/enrollment/enrollment_screen_view.h
+++ b/chrome/browser/chromeos/login/enrollment/enrollment_screen_view.h
@@ -8,6 +8,7 @@
 #include <string>
 
 #include "chrome/browser/chromeos/login/enrollment/enterprise_enrollment_helper.h"
+#include "chrome/browser/chromeos/login/oobe_screen.h"
 
 class GoogleServiceAuthError;
 
@@ -37,6 +38,8 @@ class EnrollmentScreenView {
                                            const std::string& location) = 0;
   };
 
+  constexpr static OobeScreen kScreenId = OobeScreen::SCREEN_OOBE_ENROLLMENT;
+
   virtual ~EnrollmentScreenView() {}
 
   // Initializes the view with parameters.