Run pub tests against older versions of barback.

third_party/pkg/barback-0.13.0/test/transformer/catch_asset_not_found.dart

Index: third_party/pkg/barback-0.13.0/test/transformer/catch_asset_not_found.dart
diff --git a/pkg/barback/test/transformer/catch_asset_not_found.dart b/third_party/pkg/barback-0.13.0/test/transformer/catch_asset_not_found.dart
similarity index 89%
copy from pkg/barback/test/transformer/catch_asset_not_found.dart
copy to third_party/pkg/barback-0.13.0/test/transformer/catch_asset_not_found.dart
index b43eeb753c2180c356643c85c0ee771bc3d35cc9..ee5371dff1e07927feddcf3ab8c23ef850749a70 100644
--- a/pkg/barback/test/transformer/catch_asset_not_found.dart
+++ b/third_party/pkg/barback-0.13.0/test/transformer/catch_asset_not_found.dart
@@ -7,6 +7,7 @@ library barback.test.transformer.catch_asset_not_found;
 import 'dart:async';
 
 import 'package:barback/barback.dart';
+import 'package:barback/src/utils.dart';
 
 import 'mock.dart';
 
@@ -22,7 +23,8 @@ class CatchAssetNotFoundTransformer extends MockTransformer {
   CatchAssetNotFoundTransformer(this.extension, String input)
       : input = new AssetId.parse(input);
 
-  bool doIsPrimary(AssetId id) => id.extension == extension;
+  Future<bool> doIsPrimary(AssetId id) =>
+      new Future.value(id.extension == extension);
 
   Future doApply(Transform transform) {
     return transform.getInput(input).then((_) {