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

ios/chrome/browser/signin/signin_util.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.
 
 #include "ios/chrome/browser/signin/signin_util.h"
 
 #include "base/strings/sys_string_conversions.h"
 #include "google_apis/gaia/gaia_auth_util.h"
 #import "ios/public/provider/chrome/browser/chrome_browser_provider.h"
 #import "ios/public/provider/chrome/browser/signin/chrome_identity.h"
 #include "ios/public/provider/chrome/browser/signin/signin_error_provider.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 NSArray* GetScopeArray(const std::set<std::string>& scopes) {
-  NSMutableArray* scopes_array = [[[NSMutableArray alloc] init] autorelease];
+  NSMutableArray* scopes_array = [[NSMutableArray alloc] init];
   for (const auto& scope : scopes) {
     [scopes_array addObject:base::SysUTF8ToNSString(scope)];
   }
   return scopes_array;
 }
 
 std::string GetCanonicalizedEmailForIdentity(ChromeIdentity* identity) {
   NSString* nsEmail = [identity userEmail];
   if (!nsEmail)
     return std::string();
   std::string email = base::SysNSStringToUTF8(nsEmail);
   return gaia::CanonicalizeEmail(gaia::SanitizeEmail(email));
 }
 
 bool ShouldHandleSigninError(NSError* error) {
   ios::SigninErrorProvider* provider =
       ios::GetChromeBrowserProvider()->GetSigninErrorProvider();
   return ![provider->GetSigninErrorDomain() isEqualToString:error.domain] ||
          (error.code != provider->GetCode(ios::SigninError::CANCELED) &&
           error.code !=
               provider->GetCode(ios::SigninError::HANDLED_INTERNALLY));
 }