Reorganize barback's source files.

pkg/barback/lib/src/transformer/base_transform.dart

 // Copyright (c) 2014, 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.base_transform;
+library barback.transformer.base_transform;
 
 import 'dart:async';
 
-import 'log.dart';
+import '../graph/transform_node.dart';
+import '../log.dart';
 import 'transform_logger.dart';
-import 'transform_node.dart';
 
 /// The base class for the ephemeral transform objects that are passed to
 /// transformers.
 ///
 /// This class provides the transformers with inputs, but its up to the
 /// subclasses to provide a means of emitting outputs.
 abstract class BaseTransform {
   final TransformNode _node;
 
   /// Whether the primary input should be consumed.
@@ skipping 63 matching lines @@
 
   /// Notifies the [BaseTransform] that the transformation has finished being
   /// applied.
   ///
   /// This will close any streams and release any resources that were allocated
   /// for the duration of the transformation.
   void close() {
     transform._onLogController.close();
   }
 }