Add a callback to SecureSocket for certificates that fail to be authenticated.

tests/standalone/io/secure_socket_test.dart

Index: tests/standalone/io/secure_socket_test.dart
diff --git a/tests/standalone/io/secure_socket_test.dart b/tests/standalone/io/secure_socket_test.dart
index 79bfc9b6343460374ff2bf68ac8c3804cb8ba00c..ed7abf116da23ca0704f2f4ba0166664de0a5722 100644
--- a/tests/standalone/io/secure_socket_test.dart
+++ b/tests/standalone/io/secure_socket_test.dart
@@ -26,6 +26,7 @@ void WriteAndClose(Socket socket, String message) {
 }
 
 void main() {
+  ReceivePort keepAlive = new ReceivePort();
   SecureSocket.initialize();
   // TODO(3593): Use a Dart HTTPS server for this test.
   // When we use a Dart HTTPS server, allow --short_socket_write. The flag
@@ -54,5 +55,6 @@ void main() {
   secure.onClosed = () {
     String fullPage = Strings.concatAll(chunks);
     Expect.isTrue(fullPage.contains('</body></html>'));
+    keepAlive.close();
   };
 }