Add a toString() to LogRecord.

pkg/logging/lib/logging.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.
 
 /**
  * Support for debugging and error logging.
  *
  * This library introduces abstractions similar to
  * those used in other languages, such as the Closure JS
  * Logger and java.util.logging.Logger.
@@ skipping 292 matching lines @@
   final int sequenceNumber;
 
   static int _nextNumber = 0;
 
   /** Associated exception (if any) when recording errors messages. */
   var exception;
 
   LogRecord(this.level, this.message, this.loggerName, [this.exception])
       : time = new DateTime.now(),
         sequenceNumber = LogRecord._nextNumber++;
+
+  String toString() => '[${level.name}] $loggerName: $message';
 }