[ios] Convert //ios/chrome/browser/sessions to ARC.

ios/chrome/browser/sessions/tab_restore_service_delegate_impl_ios.mm

 // Copyright 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.
 
 #include "ios/chrome/browser/sessions/tab_restore_service_delegate_impl_ios.h"
 
 #include <memory>
 #include <utility>
 
 #include "base/logging.h"
 #include "base/strings/sys_string_conversions.h"
 #include "components/sessions/core/session_types.h"
 #include "components/sessions/ios/ios_serialized_navigation_builder.h"
 #include "ios/chrome/browser/browser_state/chrome_browser_state.h"
 #import "ios/chrome/browser/tabs/tab.h"
 #import "ios/chrome/browser/tabs/tab_model.h"
 #import "ios/chrome/browser/tabs/tab_model_list.h"
 #import "ios/chrome/browser/web_state_list/web_state_list.h"
 #import "ios/web/navigation/navigation_manager_impl.h"
 #include "ios/web/public/navigation_item.h"
 #import "ios/web/web_state/web_state_impl.h"
 #import "net/base/mac/url_conversions.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 TabRestoreServiceDelegateImplIOS::TabRestoreServiceDelegateImplIOS(
     ios::ChromeBrowserState* browser_state)
     : browser_state_(browser_state) {}
 
 TabRestoreServiceDelegateImplIOS::~TabRestoreServiceDelegateImplIOS() {}
 
 TabModel* TabRestoreServiceDelegateImplIOS::tab_model() const {
   return GetLastActiveTabModelForChromeBrowserState(browser_state_);
 }
 
@@ skipping 74 matching lines @@
   Tab* tab = tab_model().currentTab;
   [tab replaceHistoryWithNavigations:navigations
                         currentIndex:selected_navigation];
   return nullptr;
 }
 
 void TabRestoreServiceDelegateImplIOS::CloseTab() {
   WebStateList* web_state_list = [tab_model() webStateList];
   web_state_list->CloseWebStateAt(web_state_list->active_index());
 }