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

ios/chrome/browser/signin/fake_oauth2_token_service_builder.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/fake_oauth2_token_service_builder.h"
 
 #include "base/memory/ptr_util.h"
 #include "components/signin/core/browser/fake_profile_oauth2_token_service.h"
 #include "components/signin/ios/browser/profile_oauth2_token_service_ios_delegate.h"
 #include "ios/chrome/browser/browser_state/chrome_browser_state.h"
 #include "ios/chrome/browser/signin/account_tracker_service_factory.h"
 #include "ios/chrome/browser/signin/profile_oauth2_token_service_ios_provider_impl.h"
 #include "ios/chrome/browser/signin/signin_client_factory.h"
 #include "ios/chrome/browser/signin/signin_error_controller_factory.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 std::unique_ptr<KeyedService> BuildFakeOAuth2TokenService(
     web::BrowserState* context) {
   ios::ChromeBrowserState* browser_state =
       ios::ChromeBrowserState::FromBrowserState(context);
   std::unique_ptr<OAuth2TokenServiceDelegate> delegate =
       base::MakeUnique<ProfileOAuth2TokenServiceIOSDelegate>(
           SigninClientFactory::GetForBrowserState(browser_state),
           base::MakeUnique<ProfileOAuth2TokenServiceIOSProviderImpl>(),
           ios::AccountTrackerServiceFactory::GetForBrowserState(browser_state),
           ios::SigninErrorControllerFactory::GetForBrowserState(browser_state));
   return base::MakeUnique<FakeProfileOAuth2TokenService>(std::move(delegate));
 }