Remove AsyncError with Expando.

utils/pub/log.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.
 
 /// Message logging.
 library log;
 
 import 'dart:async';
 
 import 'io.dart';
@@ skipping 39 matching lines @@
 
 /// A single log entry.
 class Entry {
   final Level level;
   final List<String> lines;
 
   Entry(this.level, this.lines);
 }
 
 /// Logs [message] at [Level.ERROR].
-void error(message) => write(Level.ERROR, message);
+void error(message, [error]) {
+  if (error != null) {
+    message = "$message: $error";
+    var trace = getAttachedStackTrace(error);
+    if (trace != null) {
+      message = "$message\nStackTrace: $trace";
+    }
+  }
+  write(Level.ERROR, message);
+}
 
 /// Logs [message] at [Level.WARNING].
 void warning(message) => write(Level.WARNING, message);
 
 /// Logs [message] at [Level.MESSAGE].
 void message(message) => write(Level.MESSAGE, message);
 
 /// Logs [message] at [Level.IO].
 void io(message) => write(Level.IO, message);
 
@@ skipping 150 matching lines @@
         sink.add('    | '.codeUnits);
       }
     }
 
     sink.add(line.codeUnits);
     sink.add('\n'.codeUnits);
 
     firstLine = false;
   }
 }