[ObjC ARC] Converts ios/net to ARC.

ios/net/http_response_headers_util.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/net/http_response_headers_util.h"
 
 #include <Foundation/Foundation.h>
 
 #include "base/logging.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/sys_string_conversions.h"
 #include "net/http/http_util.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 // String format used to create the http status line from the status code and
 // its localized description.
 NSString* const kHttpStatusLineFormat = @"HTTP %ld %s";
 // String format used to pass the header name/value pairs to the
 // HttpResponseHeaders.
 const char kHeaderLineFormat[] = "%s: %s";
 }
 
 namespace net {
@@ skipping 21 matching lines @@
           std::string header_line =
               base::StringPrintf(kHeaderLineFormat, header_name.c_str(),
                                  header_value.c_str());
           http_headers->AddHeader(header_line);
         }
       }];
   return http_headers;
 }
 
 }  // namespae net