Reorganize barback's source files.

pkg/barback/lib/src/graph/transformer_classifier.dart

Index: pkg/barback/lib/src/graph/transformer_classifier.dart
diff --git a/pkg/barback/lib/src/transformer_classifier.dart b/pkg/barback/lib/src/graph/transformer_classifier.dart
similarity index 94%
rename from pkg/barback/lib/src/transformer_classifier.dart
rename to pkg/barback/lib/src/graph/transformer_classifier.dart
index 344612cfd2f73f137807a01e85fc5df2605d2c8b..6ba2480085771a1114162738f38154d62d055ba2 100644
--- a/pkg/barback/lib/src/transformer_classifier.dart
+++ b/pkg/barback/lib/src/graph/transformer_classifier.dart
@@ -2,20 +2,20 @@
 // 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.transformer_classifier;
+library barback.graph.transformer_classifier;
 
 import 'dart:async';
 
-import 'asset_forwarder.dart';
-import 'asset_node.dart';
-import 'errors.dart';
-import 'log.dart';
+import '../asset/asset_forwarder.dart';
+import '../asset/asset_node.dart';
+import '../errors.dart';
+import '../log.dart';
+import '../transformer/transformer.dart';
+import '../utils.dart';
 import 'node_status.dart';
 import 'node_streams.dart';
 import 'phase.dart';
 import 'transform_node.dart';
-import 'transformer.dart';
-import 'utils.dart';
 
 /// A class for classifying the primary inputs for a transformer according to
 /// its `classifyPrimary` method.