Run pub tests against older versions of barback.

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

Index: third_party/pkg/barback-0.13.0/test/transformer/check_content_and_rename.dart
diff --git a/pkg/barback/test/transformer/check_content_and_rename.dart b/third_party/pkg/barback-0.13.0/test/transformer/check_content_and_rename.dart
similarity index 75%
copy from pkg/barback/test/transformer/check_content_and_rename.dart
copy to third_party/pkg/barback-0.13.0/test/transformer/check_content_and_rename.dart
index dffad3798e39f296680c754bfd79ecbc9decb8a4..9fcdebb6c0e50a9b14c5280fc30e36afb6d10c26 100644
--- a/pkg/barback/test/transformer/check_content_and_rename.dart
+++ b/third_party/pkg/barback-0.13.0/test/transformer/check_content_and_rename.dart
@@ -18,15 +18,11 @@ class CheckContentAndRenameTransformer extends MockTransformer {
   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);
-  }
+  CheckContentAndRenameTransformer(this.oldExtension, this.oldContent,
+      this.newExtension, this.newContent);
 
-  bool doIsPrimary(AssetId id) => id.extension == '.$oldExtension';
+  Future<bool> doIsPrimary(AssetId id) =>
+      new Future.value(id.extension != '.$oldExtension');
 
   Future doApply(Transform transform) {
     return getPrimary(transform).then((input) {