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

ios/chrome/browser/signin/authentication_service_fake.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.
 
 #import "ios/chrome/browser/signin/authentication_service_fake.h"
 
 #include <memory>
 
 #include "base/memory/ptr_util.h"
 #include "ios/chrome/browser/browser_state/chrome_browser_state.h"
 #import "ios/chrome/browser/signin/authentication_service_factory.h"
 #include "ios/chrome/browser/signin/oauth2_token_service_factory.h"
 #include "ios/chrome/browser/sync/sync_setup_service_factory.h"
 #import "ios/public/provider/chrome/browser/signin/chrome_identity.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 AuthenticationServiceFake::AuthenticationServiceFake(
     ios::ChromeBrowserState* browser_state)
     : AuthenticationService(
           browser_state,
           OAuth2TokenServiceFactory::GetForBrowserState(browser_state),
           SyncSetupServiceFactory::GetForBrowserState(browser_state)),
       have_accounts_changed_(false) {}
 
 AuthenticationServiceFake::~AuthenticationServiceFake() {}
 
 void AuthenticationServiceFake::SignIn(ChromeIdentity* identity,
                                        const std::string& hosted_domain) {
-  authenticated_identity_.reset([identity retain]);
+  authenticated_identity_ = identity;
 }
 
 void AuthenticationServiceFake::SignOut(
     signin_metrics::ProfileSignout signout_source,
     ProceduralBlock completion) {
-  authenticated_identity_.reset();
+  authenticated_identity_ = nil;
   if (completion)
     completion();
 }
 
 void AuthenticationServiceFake::SetHaveAccountsChanged(bool changed) {
   have_accounts_changed_ = changed;
 }
 
 bool AuthenticationServiceFake::HaveAccountsChanged() {
   return have_accounts_changed_;
 }
 
 bool AuthenticationServiceFake::IsAuthenticated() {
-  return authenticated_identity_.get();
+  return authenticated_identity_ != nil;
 }
 
 ChromeIdentity* AuthenticationServiceFake::GetAuthenticatedIdentity() {
   return authenticated_identity_;
 }
 
 NSString* AuthenticationServiceFake::GetAuthenticatedUserEmail() {
   return [authenticated_identity_ userEmail];
 }
 
 std::unique_ptr<KeyedService>
 AuthenticationServiceFake::CreateAuthenticationService(
     web::BrowserState* browser_state) {
   return base::WrapUnique(new AuthenticationServiceFake(
       ios::ChromeBrowserState::FromBrowserState(browser_state)));
 }