Remove AsyncError with Expando.

tools/testing/dart/utils.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.
 
 library utils;
 
 import 'dart:io';
+import 'dart:async' show getAttachedStackTrace;
 import 'dart:utf' as utf;
 
 class DebugLogger {
   static IOSink _sink;
 
   /**
    * If [path] was null, the DebugLogger will write messages to stdout.
    */
   static init(Path path, {append: false}) {
     if (path != null) {
       var mode = append ? FileMode.APPEND : FileMode.WRITE;
       _sink = new File.fromPath(path).openWrite(mode: mode);
     }
   }
 
   static void close() {
     if (_sink != null) {
       _sink.close();
       _sink = null;
     }
   }
 
-  static void info(String msg) {
+  static String _formatErrorMessage(String msg, error) {
+    if (error == null) return msg;
+    msg += ": $error";
+    var trace = getAttachedStackTrace(error);
+    if (trace != null) msg += "\nStackTrace: $trace";
+    return msg;
+  }
+  static void info(String msg, [error]) {
+    msg = _formatErrorMessage(msg, error);
     _print("Info: $msg");
   }
 
-  static void warning(String msg) {
+  static void warning(String msg, [error]) {
+    msg = _formatErrorMessage(msg, error);
     _print("Warning: $msg");
   }
 
-  static void error(String msg) {
+  static void error(String msg, [error]) {
+    msg = _formatErrorMessage(msg, error);
     _print("Error: $msg");
   }
 
   static void _print(String msg) {
     if (_sink != null) {
       _sink.writeln(msg);
     } else {
       print(msg);
     }
   }
 }
 
 List<int> encodeUtf8(String string) {
   return utf.encodeUtf8(string);
 }
 
 // TODO(kustermann,ricow): As soon we have a debug log we should log
 // invalid utf8-encoded input to the log.
 // Currently invalid bytes will be replaced by a replacement character.
 String decodeUtf8(List<int> bytes) {
   return utf.decodeUtf8(bytes);
 }