Remove AsyncError with Expando.

tests/standalone/io/dart_std_io_pipe_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 //
 // Test a dart sub-process handling stdio with different types of
 // redirection.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
@@ skipping 75 matching lines @@
 
       // Cleanup test directory.
       dir.deleteSync(recursive: true);
     });
     // Drain out and err streams so they close.
     process.stdout.listen((_) {});
     process.stderr.listen((_) {});
   });
   future.catchError((error) {
     dir.deleteSync(recursive: true);
-    Expect.fail(error.error.toString());
+    Expect.fail(error.toString());
   });
 }
 
 // This tests that the Dart standalone VM can handle piping to stdin
 // and can pipe to stdout.
 main() {
   // Don't try to run shell scripts on Windows.
   var os = Platform.operatingSystem;
   if (os == 'windows') return;
 
@@ skipping 11 matching lines @@
   }
 
   // Run the shell script.
   test(shellScript.path, scriptFile.path, "0", false);
   test(shellScript.path, scriptFile.path, "0", true);
   test(shellScript.path, scriptFile.path, "1", false);
   test(shellScript.path, scriptFile.path, "1", true);
   test(shellScript.path, scriptFile.path, "2", false);
   test(shellScript.path, scriptFile.path, "2", true);
 }