cros: Break BaseScreenHandler into two classes.

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

 // Copyright (c) 2012 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_BASE_SCREEN_H_
 #define CHROME_BROWSER_CHROMEOS_LOGIN_SCREENS_BASE_SCREEN_H_
 
 #include <string>
 
 #include "base/gtest_prod_util.h"
@@ skipping 113 matching lines @@
   FRIEND_TEST_ALL_PREFIXES(EnrollmentScreenTest, TestCancel);
   FRIEND_TEST_ALL_PREFIXES(EnrollmentScreenTest, TestSuccess);
   FRIEND_TEST_ALL_PREFIXES(AttestationAuthEnrollmentScreenTest, TestCancel);
   FRIEND_TEST_ALL_PREFIXES(ForcedAttestationAuthEnrollmentScreenTest,
                            TestCancel);
   FRIEND_TEST_ALL_PREFIXES(MultiAuthEnrollmentScreenTest, TestCancel);
   FRIEND_TEST_ALL_PREFIXES(ProvisionedEnrollmentScreenTest, TestBackButton);
   FRIEND_TEST_ALL_PREFIXES(HandsOffNetworkScreenTest, RequiresNoInput);
   FRIEND_TEST_ALL_PREFIXES(HandsOffNetworkScreenTest, ContinueClickedOnlyOnce);
 
-  friend class BaseScreenHandler;
+  friend class BaseWebUIHandler;
   friend class NetworkScreenTest;
   friend class ScreenEditor;
   friend class ScreenManager;
   friend class UpdateScreenTest;
 
   void SetContext(::login::ScreenContext* context);
 
   // Called when context for the current screen was
   // changed. Notification about this event comes from the JS
   // counterpart.
   void OnContextChanged(const base::DictionaryValue& diff);
 
   ModelViewChannel* channel_ = nullptr;
 
   BaseScreenDelegate* base_screen_delegate_ = nullptr;
 
   const OobeScreen screen_id_;
 
   DISALLOW_COPY_AND_ASSIGN(BaseScreen);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_SCREENS_BASE_SCREEN_H_