Generate an error for active connections when the HTTP client is shutdown

tests/standalone/io/http_connection_close_test.dart

Index: tests/standalone/io/http_connection_close_test.dart
diff --git a/tests/standalone/io/http_connection_close_test.dart b/tests/standalone/io/http_connection_close_test.dart
index b11499b7dbf385a10922001573545cba3710bfe9..c46dd417a4fb0f25be4f95aafee45e9b690f516f 100644
--- a/tests/standalone/io/http_connection_close_test.dart
+++ b/tests/standalone/io/http_connection_close_test.dart
@@ -66,10 +66,11 @@ void testStreamResponse() {
     resp.inputStream.onData = () {
       bytes += resp.inputStream.read().length;
       if (bytes > 100) {
-        client.shutdown();
+        client.shutdown(force: true);
       }
     };
   };
+  connection.onError = (e) => Expect.isTrue(e is HttpException);
 }
 
 main() {