Add a bunch of toString methods to internal Barback classes.

pkg/barback/lib/src/transform_node.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.transform_node;
 
 import 'dart:async';
 
 import 'package:source_maps/span.dart';
 
@@ skipping 15 matching lines @@
 class TransformNode {
   /// The [Phase] that this transform runs in.
   final Phase phase;
 
   /// The [Transformer] to apply to this node's inputs.
   final Transformer transformer;
 
   /// The node for the primary asset this transform depends on.
   final AssetNode primary;
 
+  /// A string describing the location of [this] in the transformer graph.
+  final String _location;
+
   /// The subscription to [primary]'s [AssetNode.onStateChange] stream.
   StreamSubscription _primarySubscription;
 
   /// True if an input has been modified since the last time this transform
   /// began running.
   bool get isDirty => _isDirty;
   var _isDirty = true;
 
   /// The subscriptions to each input's [AssetNode.onStateChange] stream.
   var _inputSubscriptions = new Map<AssetId, StreamSubscription>();
@@ skipping 11 matching lines @@
   final _onDirtyController = new StreamController.broadcast(sync: true);
 
   /// A stream that emits an event whenever this transform logs an entry.
   ///
   /// This is synchronous because error logs can cause the transform to fail, so
   /// we need to ensure that their processing isn't delayed until after the
   /// transform or build has finished.
   Stream<LogEntry> get onLog => _onLogController.stream;
   final _onLogController = new StreamController<LogEntry>.broadcast(sync: true);
 
-  TransformNode(this.phase, this.transformer, this.primary) {
+  TransformNode(this.phase, this.transformer, this.primary, this._location) {
     _primarySubscription = primary.onStateChange.listen((state) {
       if (state.isRemoved) {
         remove();
       } else {
         _dirty();
       }
     });
   }
 
   /// The [TransformInfo] describing this node.
@@ skipping 134 matching lines @@
 
     return brandNewOutputs;
   }
 
   void _log(AssetId asset, LogLevel level, String message, Span span) {
     // If the log isn't already associated with an asset, use the primary.
     if (asset == null) asset = primary.id;
     var entry = new LogEntry(info, asset, level, message, span);
     _onLogController.add(entry);
   }
+
+  String toString() =>
+    "transform node in $_location for $transformer on $primary";
 }