[ObjC ARC] Converts ios/net to ARC.

ios/net/cookies/cookie_store_ios_client.mm

 // Copyright 2014 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/net/cookies/cookie_store_ios_client.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 // The CookieStoreIOSClient.
 net::CookieStoreIOSClient* g_client;
 }  // namespace
 
 namespace net {
 
 void SetCookieStoreIOSClient(CookieStoreIOSClient* client) {
   g_client = client;
 }
 
 CookieStoreIOSClient* GetCookieStoreIOSClient() {
   return g_client;
 }
 
 CookieStoreIOSClient::CookieStoreIOSClient() {}
 
 CookieStoreIOSClient::~CookieStoreIOSClient() {}
 
 void CookieStoreIOSClient::WillChangeCookieStorage() const {}
 
 void CookieStoreIOSClient::DidChangeCookieStorage() const {}
 
 scoped_refptr<base::SequencedTaskRunner>
 CookieStoreIOSClient::GetTaskRunner() const {
   return scoped_refptr<base::SequencedTaskRunner>();
 }
 
 }  // namespace net