Close HttpServer in WebSocket tests.

tests/standalone/io/web_socket_test.dart

Index: tests/standalone/io/web_socket_test.dart
diff --git a/tests/standalone/io/web_socket_test.dart b/tests/standalone/io/web_socket_test.dart
index c20ee068cb1063a77fa5616a6093dff5294c0786..7ac1e414ae94e4c5a7534d9f1eb7c0cf5aadc892 100644
--- a/tests/standalone/io/web_socket_test.dart
+++ b/tests/standalone/io/web_socket_test.dart
@@ -167,6 +167,7 @@ class SecurityConfiguration {
   void testDoubleCloseClient() {
     createServer().then((server) {
       server.transform(new WebSocketTransformer()).listen((webSocket) {
+        server.close();
         webSocket.listen((event) {
           if (event is CloseEvent) {
             webSocket.close();
@@ -189,6 +190,7 @@ class SecurityConfiguration {
   void testDoubleCloseServer() {
     createServer().then((server) {
       server.transform(new WebSocketTransformer()).listen((webSocket) {
+        server.close();
         webSocket.listen((event) {
           if (event is CloseEvent) {
             webSocket.close();