Implement simple http server with set cookie functionality.

ios/web/public/test/response_providers/response_provider.mm

Index: ios/web/public/test/response_providers/response_provider.mm
diff --git a/ios/web/public/test/response_providers/response_provider.mm b/ios/web/public/test/response_providers/response_provider.mm
index e795e95bd0e6655ebeee4e106a3f437361dab428..00436cd6ba80861d4c6eebce08c0f35bda2188d5 100644
--- a/ios/web/public/test/response_providers/response_provider.mm
+++ b/ios/web/public/test/response_providers/response_provider.mm
@@ -51,6 +51,14 @@
 
 // static
 scoped_refptr<net::HttpResponseHeaders>
+ResponseProvider::GetDefaultResponseHeaders(const std::string& cookie) {
+  scoped_refptr<net::HttpResponseHeaders> result = GetDefaultResponseHeaders();
+  result->AddCookie(cookie);
+  return result;
+}
+
+// static
+scoped_refptr<net::HttpResponseHeaders>
 ResponseProvider::GetRedirectResponseHeaders(
     const std::string& destination,
     const net::HttpStatusCode& http_status) {