Expand barback's notion of dirtiness to understand declaredness.

pkg/barback/test/transformer/declaring_check_content_and_rename.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.test.transformer.declaring_check_content_and_rename;
+
+import 'dart:async';
+
+import 'package:barback/barback.dart';
+
+import 'check_content_and_rename.dart';
+
+class DeclaringCheckContentAndRenameTransformer
+    extends CheckContentAndRenameTransformer
+    implements DeclaringTransformer {
+  DeclaringCheckContentAndRenameTransformer(String oldExtension,
+        String oldContent, String newExtension, String newContent)
+      : super(oldExtension, oldContent, newExtension, newContent);
+
+  void declareOutputs(DeclaringTransform transform) {
+    transform.declareOutput(
+        transform.primaryId.changeExtension('.$newExtension'));
+  }
+}