Remove barback from the repo.

pkg/barback/test/transformer/check_content_and_rename.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.test.transformer.check_content_and_rename;
-
-import 'dart:async';
-
-import 'package:barback/barback.dart';
-
-import 'mock.dart';
-
-/// A transformer that checks the extension and content of an asset, then
-/// produces a new asset with a new extension and new content.
-class CheckContentAndRenameTransformer extends MockTransformer {
-  final String oldExtension;
-  final String oldContent;
-  final String newExtension;
-  final String newContent;
-
-  CheckContentAndRenameTransformer({this.oldExtension, this.oldContent,
-      this.newExtension, this.newContent}) {
-    assert(oldExtension != null);
-    assert(oldContent != null);
-    assert(newExtension != null);
-    assert(newContent != null);
-  }
-
-  bool doIsPrimary(AssetId id) => id.extension == '.$oldExtension';
-
-  Future doApply(Transform transform) {
-    return getPrimary(transform).then((input) {
-      return input.readAsString().then((contents) {
-        if (contents != oldContent) return;
-
-        transform.addOutput(new Asset.fromString(
-            input.id.changeExtension('.$newExtension'), newContent));
-      });
-    });
-  }
-}