Add Observatory test of io.

tests/standalone/io/raw_socket_test.dart

Index: tests/standalone/io/raw_socket_test.dart
diff --git a/tests/standalone/io/raw_socket_test.dart b/tests/standalone/io/raw_socket_test.dart
index bc537f516ce2740db2331b99df3065349aaca1f3..4acc6ee9503a32ed0f7b6d8494618989a4c20c49 100644
--- a/tests/standalone/io/raw_socket_test.dart
+++ b/tests/standalone/io/raw_socket_test.dart
@@ -23,6 +23,7 @@ void testSimpleBind() {
   asyncStart();
   RawServerSocket.bind(InternetAddress.LOOPBACK_IP_V4, 0).then((s) {
     Expect.isTrue(s.port > 0);
+    s.close();
     asyncEnd();
   });
 }
@@ -56,6 +57,7 @@ void testInvalidBind() {
             })
             .catchError((error) {
               Expect.isTrue(error is SocketException);
+              s.close();
               asyncEnd();
             });
       });