Remove AsyncError with Expando.

tests/standalone/io/raw_secure_socket_pause_test.dart

Index: tests/standalone/io/raw_secure_socket_pause_test.dart
diff --git a/tests/standalone/io/raw_secure_socket_pause_test.dart b/tests/standalone/io/raw_secure_socket_pause_test.dart
index d70311299f264402bb8c79088614b651912e8b06..cfd93cb721528bd51e9095651bbd2968d5ed83eb 100644
--- a/tests/standalone/io/raw_secure_socket_pause_test.dart
+++ b/tests/standalone/io/raw_secure_socket_pause_test.dart
@@ -100,8 +100,11 @@ void main() {
               default: throw "Unexpected event $event";
             }
           },
-          onError: (AsyncError a) {
-            Expect.fail("onError handler of RawSecureSocket stream hit: $a");
+          onError: (e) {
+            String msg = "onError handler of RawSecureSocket stream hit: $e";
+            var trace = getAttachedStackTrace(e);
+            if (trace != null) msg += "\nStackTrace: $trace";
+            Expect.fail(msg);
           });
     });
   });