[ObjC ARC] Converts ios/chrome/browser/signin:signin to ARC.

ios/chrome/browser/signin/signin_client_impl.mm

 // Copyright 2015 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/signin/signin_client_impl.h"
 
 #include <stddef.h>
 
 #include <utility>
 
@@ skipping 18 matching lines @@
 #include "ios/chrome/browser/browser_state/chrome_browser_state_manager.h"
 #include "ios/chrome/browser/content_settings/cookie_settings_factory.h"
 #include "ios/chrome/browser/content_settings/host_content_settings_map_factory.h"
 #include "ios/chrome/browser/signin/gaia_auth_fetcher_ios.h"
 #include "ios/chrome/browser/web_data_service_factory.h"
 #include "ios/chrome/common/channel_info.h"
 #include "ios/public/provider/chrome/browser/chrome_browser_provider.h"
 #include "net/url_request/url_request_context_getter.h"
 #include "url/gurl.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 SigninClientImpl::SigninClientImpl(
     ios::ChromeBrowserState* browser_state,
     SigninErrorController* signin_error_controller)
     : OAuth2TokenService::Consumer("signin_client_impl"),
       browser_state_(browser_state),
       signin_error_controller_(signin_error_controller) {
   signin_error_controller_->AddObserver(this);
   net::NetworkChangeNotifier::AddNetworkChangeObserver(this);
 }
 
@@ skipping 184 matching lines @@
   }
 }
 
 std::unique_ptr<GaiaAuthFetcher> SigninClientImpl::CreateGaiaAuthFetcher(
     GaiaAuthConsumer* consumer,
     const std::string& source,
     net::URLRequestContextGetter* getter) {
   return base::MakeUnique<GaiaAuthFetcherIOS>(consumer, source, getter,
                                               browser_state_);
 }