[ObjC ARC] Converts ios/web/public/test/http_server:http_server to ARC.

ios/web/public/test/http_server/http_auth_response_provider.mm

 // Copyright 2017 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/web/public/test/http_server/http_auth_response_provider.h"
 
 #include "base/base64.h"
 #include "base/strings/stringprintf.h"
 #include "net/http/http_request_headers.h"
 #include "net/http/http_response_headers.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace web {
 
 HttpAuthResponseProvider::HttpAuthResponseProvider(const GURL& url,
                                                    const std::string& realm,
                                                    const std::string& username,
                                                    const std::string& password)
     : url_(url), realm_(realm), username_(username), password_(password) {}
 
 HttpAuthResponseProvider::~HttpAuthResponseProvider() = default;
 
@@ skipping 22 matching lines @@
     std::string auth =
         base::StringPrintf("%s:%s", username_.c_str(), password_.c_str());
     std::string encoded_auth;
     base::Base64Encode(auth, &encoded_auth);
     return header == base::StringPrintf("Basic %s", encoded_auth.c_str());
   }
   return false;
 }
 
 }  // namespace web