Remove AsyncError with Expando.

tests/standalone/io/file_test.dart

 // Copyright (c) 2013, 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.
 //
 // Dart test program for testing file I/O.
 
 import "package:expect/expect.dart";
 import 'dart:async';
 import 'dart:io';
 import 'dart:isolate';
@@ skipping 134 matching lines @@
       });
 
       // Immediate read should read 0 bytes.
       input.listen(
         (d) {
           for (int i = 0; i < d.length; ++i) {
             Expect.equals(buffer[(i + position) % buffer.length], d[i]);
           }
           position += d.length;
         },
-        onError: (e) {
+        onError: (error) {
           print('Error on input in testReadWriteStreamLargeFile');
-          print('with error $e');
-          throw e;
+          print('with error $error');
+          var trace = getAttachedStackTrace(error);
+          if (trace != null) print("StackTrace: $trace");
+          throw error;
         },
         onDone: () {
           Expect.equals(expectedLength, position);
           testPipe(file, buffer)
               .then((_) => file.delete())
               .then((_) {
                   asyncTestDone('testReadWriteStreamLargeFile: main test');
               })
               .catchError((e) {
                 print('Exception while deleting ReadWriteStreamLargeFile file');
                 print('Exception $e');
+                var trace = getAttachedStackTrace(e);
+                if (trace != null) print("StackTrace: $trace");
               });
         });
     });
   }
 
   static Future testPipe(File file, buffer) {
     String outputFilename = '${file.path}_copy';
     File outputFile = new File(outputFilename);
     var input = file.openRead();
     var output = outputFile.openWrite();
@@ skipping 1057 matching lines @@
       testDirectorySync();
       testWriteStringUtf8();
       testWriteStringUtf8Sync();
     });
   }
 }
 
 main() {
   FileTest.testMain();
 }