Revise barback logging patch.

pkg/barback/lib/src/barback.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;
 
 import 'dart:async';
 
 import 'asset.dart';
 import 'asset_id.dart';
 import 'asset_set.dart';
-import 'barback_logger.dart';
+import 'log.dart';
 import 'build_result.dart';
 import 'errors.dart';
 import 'package_graph.dart';
 import 'package_provider.dart';
 import 'transformer.dart';
 
 /// A general-purpose asynchronous build dependency graph manager.
 ///
 /// It consumes source assets (including Dart files) in a set of packages,
 /// runs transformations on them, and then tracks which sources have been
@@ skipping 35 matching lines @@
 
   /// A stream that emits any errors from the graph or the transformers.
   ///
   /// This emits errors as they're detected. If an error occurs in one part of
   /// the graph, unrelated parts will continue building.
   ///
   /// This will not emit programming errors from barback itself. Those will be
   /// emitted through the [results] stream's error channel.
   Stream get errors => _graph.errors;
 
-  Barback(PackageProvider provider, {BarbackLogger logger})
-      : _graph = new PackageGraph(provider, logger: logger);
+  /// The stream of [LogEntry] objects used to report transformer log entries.
+  ///
+  /// If this stream has listeners, then log entries will go to that.
+  /// Otherwise, a default logger will display them.
+  Stream<LogEntry> get log => _graph.log;
+
+  Barback(PackageProvider provider)
+      : _graph = new PackageGraph(provider);
 
   /// Gets the asset identified by [id].
   ///
   /// If [id] is for a generated or transformed asset, this will wait until
   /// it has been created and return it. If the asset cannot be found, throws
   /// [AssetNotFoundException].
   Future<Asset> getAssetById(AssetId id) {
     return _graph.getAssetNode(id).then((node) {
       if (node == null) throw new AssetNotFoundException(id);
       return node.asset;
@@ skipping 23 matching lines @@
   ///
   /// To the extent that [transformers] is similar to the previous transformer
   /// phases for [package], the existing asset graph will be preserved.
   ///
   /// Elements of the inner iterable of [transformers] must be either
   /// [Transformer]s or [TransformerGroup]s.
   void updateTransformers(String package,
           Iterable<Iterable> transformers) =>
       _graph.updateTransformers(package, transformers);
 }