[ObjC ARC] Converts ios/web:web to ARC.

ios/web/web_state/web_state_impl.mm

 // Copyright 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.
 
 #import "ios/web/web_state/web_state_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include "base/logging.h"
@@ skipping 20 matching lines @@
 #include "ios/web/public/webui/web_ui_ios_controller.h"
 #include "ios/web/web_state/global_web_state_event_tracker.h"
 #import "ios/web/web_state/navigation_context_impl.h"
 #import "ios/web/web_state/session_certificate_policy_cache_impl.h"
 #import "ios/web/web_state/ui/crw_web_controller.h"
 #import "ios/web/web_state/ui/crw_web_controller_container_view.h"
 #include "ios/web/webui/web_ui_ios_controller_factory_registry.h"
 #include "ios/web/webui/web_ui_ios_impl.h"
 #include "net/http/http_response_headers.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace web {
 
 /* static */
 std::unique_ptr<WebState> WebState::Create(const CreateParams& params) {
   std::unique_ptr<WebStateImpl> web_state(new WebStateImpl(params));
 
   // Initialize the new session.
   web_state->GetNavigationManagerImpl().InitializeSession();
 
   // TODO(crbug.com/703565): remove std::move() once Xcode 9.0+ is required.
@@ skipping 104 matching lines @@
 bool WebStateImpl::Configured() const {
   return web_controller_ != nil;
 }
 
 CRWWebController* WebStateImpl::GetWebController() {
   return web_controller_;
 }
 
 void WebStateImpl::SetWebController(CRWWebController* web_controller) {
   [web_controller_ close];
-  web_controller_.reset([web_controller retain]);
+  web_controller_.reset(web_controller);
 }
 
 void WebStateImpl::OnTitleChanged() {
   for (auto& observer : observers_)
     observer.TitleWasSet();
 }
 
 void WebStateImpl::OnVisibleSecurityStateChange() {
   for (auto& observer : observers_)
     observer.DidChangeVisibleSecurityState();
@@ skipping 533 matching lines @@
     const LoadCommittedDetails& load_details) {
   for (auto& observer : observers_)
     observer.NavigationItemCommitted(load_details);
 }
 
 WebState* WebStateImpl::GetWebState() {
   return this;
 }
 
 }  // namespace web