Expanding WebSocket test

tests/html/websocket_test.dart

Index: tests/html/websocket_test.dart
diff --git a/tests/html/websocket_test.dart b/tests/html/websocket_test.dart
index 1738ecec8e1769f5d690c7252fca7d125a1e565d..752856c25199c5b8be55939df68688694667b6f3 100644
--- a/tests/html/websocket_test.dart
+++ b/tests/html/websocket_test.dart
@@ -24,5 +24,18 @@ main() {
         expect(socket, isWebSocket);
         }, expectation);
     });
+
+    if (WebSocket.supported) {
+      test('echo', () {
+        var socket = new WebSocket('ws://${window.location.host}/ws', 'chat');
+        socket.onOpen.first.then((_) {
+          socket.send('hello!');
+        });
+
+        return socket.onMessage.first.then((MessageEvent e) {
+          expect(e.data, 'hello!');
+        });
+      });
+    }
   });
 }