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

ios/public/provider/chrome/browser/signin/signin_error_provider.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/public/provider/chrome/browser/signin/signin_error_provider.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace ios {
 
 SigninErrorProvider::SigninErrorProvider() {}
 
 SigninErrorProvider::~SigninErrorProvider() {}
 
 SigninErrorCategory SigninErrorProvider::GetErrorCategory(NSError* error) {
   return SigninErrorCategory::UNKNOWN_ERROR;
 }
 
@@ skipping 15 matching lines @@
 
 NSString* SigninErrorProvider::GetSigninErrorDomain() {
   return @"signin_error_domain";
 }
 
 int SigninErrorProvider::GetCode(SigninError error) {
   return 0;
 }
 
 }  // namesace ios