Ability to add ResponseProvider

ios/web/public/test/http_server_util.mm

Index: ios/web/public/test/http_server_util.mm
diff --git a/ios/web/public/test/http_server_util.mm b/ios/web/public/test/http_server_util.mm
index 7be13c2a50c12c11170315163088e389e1fc7c98..7b032bcc81613bfa3d15caddaf9bd50b048687b4 100644
--- a/ios/web/public/test/http_server_util.mm
+++ b/ios/web/public/test/http_server_util.mm
@@ -31,5 +31,11 @@ void SetUpHttpServer(std::unique_ptr<web::ResponseProvider> provider) {
   server.AddResponseProvider(std::move(provider));
 }
 
+void AddResponseProvider(std::unique_ptr<web::ResponseProvider> provider) {
+  web::test::HttpServer& server = web::test::HttpServer::GetSharedInstance();
+  DCHECK(server.IsRunning());
+  server.AddResponseProvider(std::move(provider));
+}
+
 }  // namespace test
 }  // namespace web