Add a bunch of toString methods to internal Barback classes.

pkg/barback/lib/src/group_runner.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.group_runner;
 
 import 'dart:async';
 
 import 'asset_cascade.dart';
 import 'asset_node.dart';
 import 'log.dart';
 import 'phase.dart';
 import 'stream_pool.dart';
 import 'transformer_group.dart';
 
-/// A class that process all of the phases in a single transformer group.
+/// A class that processes all of the phases in a single transformer group.
 ///
 /// A group takes many inputs, processes them, and emits many outputs.
 class GroupRunner {
+  /// The group this runner runs.
+  final TransformerGroup _group;
+
+  /// A string describing the location of [this] in the transformer graph.
+  final String _location;
+
   /// The phases defined by this group.
   final _phases = new List<Phase>();
 
   /// A stream that emits an event whenever this group becomes dirty and needs
   /// to be run.
   ///
   /// This may emit events when the group was already dirty or while processing
   /// transforms. Events are emitted synchronously to ensure that the dirty
   /// state is thoroughly propagated as soon as any assets are changed.
   Stream get onDirty => _onDirtyPool.stream;
   final _onDirtyPool = new StreamPool.broadcast();
 
   /// Whether this group is dirty and needs to be run.
   bool get isDirty => _phases.any((phase) => phase.isDirty);
 
   /// A stream that emits an event whenever any transforms in this group logs
   /// an entry.
   Stream<LogEntry> get onLog => _onLogPool.stream;
   final _onLogPool = new StreamPool<LogEntry>.broadcast();
 
   // TODO(nweiz): move to a more push-based way of propagating outputs and get
   // rid of this. Once that's done, see if we can unify GroupRunner and
   // AssetCascade.
   /// The set of outputs that has been returned by [process].
   ///
   /// [process] is expected to only return new outputs, so this is used to
   /// ensure that it does so.
   final _alreadyEmittedOutputs = new Set<AssetNode>();
 
-  GroupRunner(AssetCascade cascade, TransformerGroup group) {
-    var lastPhase = new Phase(cascade, group.phases.first);
+  GroupRunner(AssetCascade cascade, this._group, this._location) {
+    var lastPhase = new Phase(cascade, _group.phases.first, _location);
     _phases.add(lastPhase);
-    for (var phase in group.phases.skip(1)) {
+    for (var phase in _group.phases.skip(1)) {
       lastPhase = lastPhase.addPhase(phase);
       _phases.add(lastPhase);
     }
 
     for (var phase in _phases) {
       _onDirtyPool.add(phase.onDirty);
       _onLogPool.add(phase.onLog);
     }
   }
 
@@ skipping 21 matching lines @@
     // If we get here, all phases are done processing.
     var newOutputs = _phases.last.availableOutputs
         .difference(_alreadyEmittedOutputs);
     for (var output in newOutputs) {
       output.whenRemoved(() => _alreadyEmittedOutputs.remove(output));
     }
     _alreadyEmittedOutputs.addAll(newOutputs);
 
     return new Future.value(newOutputs);
   }
+
+  String toString() => "group in phase $_location for $_group";
 }