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

tests/standalone/io/secure_builtin_roots_test.dart

Index: tests/standalone/io/secure_builtin_roots_test.dart
diff --git a/tests/standalone/io/secure_builtin_roots_test.dart b/tests/standalone/io/secure_builtin_roots_test.dart
index 176f6ee83762fe5fd30aca4a16f1f50d8f0b3ae2..386dd75dddd5f43bd3e5647f465597ed882a2054 100644
--- a/tests/standalone/io/secure_builtin_roots_test.dart
+++ b/tests/standalone/io/secure_builtin_roots_test.dart
@@ -7,6 +7,7 @@ import "dart:uri";
 import "dart:isolate";
 
 void testGoogleUrl() {
+  ReceivePort keepAlive = new ReceivePort();
   HttpClient client = new HttpClient();
 
   void testUrl(String url) {
@@ -24,6 +25,7 @@ void testGoogleUrl() {
       };
       response.inputStream.onClosed = () {
         client.shutdown();
+        keepAlive.close();
       };
     };
     conn.onError = (error) => Expect.fail("Unexpected IO error $error");