cros: Break BaseScreenHandler into two classes.

chrome/browser/ui/webui/chromeos/login/user_board_screen_handler.cc

 // 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.
 
 #include "chrome/browser/ui/webui/chromeos/login/user_board_screen_handler.h"
 
 #include "chrome/browser/chromeos/login/screens/user_selection_screen.h"
 #include "components/login/localized_values_builder.h"
 
 namespace chromeos {
 
-UserBoardScreenHandler::UserBoardScreenHandler() : weak_factory_(this) {}
+UserBoardScreenHandler::UserBoardScreenHandler()
+    : BaseScreenHandler(kScreenId), weak_factory_(this) {}
 
 UserBoardScreenHandler::~UserBoardScreenHandler() {
 }
 
 void UserBoardScreenHandler::DeclareLocalizedValues(
     ::login::LocalizedValuesBuilder* builder) {
 }
 
 void UserBoardScreenHandler::RegisterMessages() {
   AddCallback("getUsers", &UserBoardScreenHandler::HandleGetUsers);
@@ skipping 65 matching lines @@
 void UserBoardScreenHandler::SetAuthType(
     const AccountId& account_id,
     proximity_auth::ScreenlockBridge::LockHandler::AuthType auth_type,
     const base::string16& initial_value) {
   CallJS("login.AccountPickerScreen.setAuthType", account_id,
          static_cast<int>(auth_type), base::StringValue(initial_value));
 }
 
 void UserBoardScreenHandler::Bind(UserSelectionScreen* screen) {
   screen_ = screen;
-  BaseScreenHandler::SetBaseScreen(screen_);
+  BaseWebUIHandler::SetBaseScreen(screen_);
 }
 
 void UserBoardScreenHandler::Unbind() {
   screen_ = nullptr;
-  BaseScreenHandler::SetBaseScreen(nullptr);
+  BaseWebUIHandler::SetBaseScreen(nullptr);
 }
 
 base::WeakPtr<UserBoardView> UserBoardScreenHandler::GetWeakPtr() {
   return weak_factory_.GetWeakPtr();
 }
 
 }  // namespace chromeos