Revise barback logging patch.

pkg/barback/lib/src/barback_logger.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 barback.barback_logger;
-
-import 'package:source_maps/span.dart';
-
-import 'asset_id.dart';
-import 'errors.dart';
-
-/// Object used to report warnings and errors encountered while running a
-/// transformer.
-class BarbackLogger {
-  /// Logs [entry].
-  void logEntry(LogEntry entry) {
-    var buffer = new StringBuffer();
-    buffer.write("[${entry.level} ${entry.transform}] ");
-
-    var message = entry.message;
-    if (entry.span == null) {
-      buffer.write(entry.span.getLocationMessage(entry.message));
-    } else {
-      buffer.write(message);
-    }
-
-    print(buffer);
-  }
-}
-
-/// The severity of a logged message.
-class LogLevel {
-  static const INFO = const LogLevel("Info");
-  static const WARNING = const LogLevel("Warning");
-  static const ERROR = const LogLevel("Error");
-
-  final String name;
-  const LogLevel(this.name);
-
-  String toString() => name;
-}
-
-/// One message logged during a transform.
-class LogEntry {
-  /// The transform that logged the message.
-  final TransformInfo transform;
-
-  /// The asset that the message is associated with.
-  final AssetId asset;
-
-  final LogLevel level;
-  final String message;
-
-  /// The location that the message pertains to or null if not associated with
-  /// a source [Span].
-  final Span span;
-
-  LogEntry(this.transform, this.asset, this.level, this.message, this.span);
-}