Run pub tests against older versions of barback.

third_party/pkg/barback-0.13.0/test/package_graph/group_test.dart

Index: third_party/pkg/barback-0.13.0/test/package_graph/group_test.dart
diff --git a/pkg/barback/test/package_graph/group_test.dart b/third_party/pkg/barback-0.13.0/test/package_graph/group_test.dart
similarity index 96%
copy from pkg/barback/test/package_graph/group_test.dart
copy to third_party/pkg/barback-0.13.0/test/package_graph/group_test.dart
index 4e2cb443d665e312fc29905504c974947f645fd8..468cb8c249f91503d573636a63d3abd32d4babb6 100644
--- a/pkg/barback/test/package_graph/group_test.dart
+++ b/third_party/pkg/barback-0.13.0/test/package_graph/group_test.dart
@@ -449,25 +449,4 @@ main() {
     updateSources(["app|foo.a", "app|foo.x"]);
     buildShouldFail([isAssetCollisionException("app|foo.c")]);
   });
-
-  // Regression test for issue 18872.
-  test("a multi-phase group's outputs should be visible as secondary inputs "
-      "for a following group", () {
-    initGraph({
-      "app|foo.txt": "bar.c",
-      "app|bar.a": "bar"
-    }, {"app": [
-      [new TransformerGroup([
-        [new RewriteTransformer("a", "b")],
-        [new RewriteTransformer("b", "c")]
-      ])],
-      [new TransformerGroup([
-        [new ManyToOneTransformer("txt")]
-      ])]
-    ]});
-
-    updateSources(["app|foo.txt", "app|bar.a"]);
-    expectAsset("app|foo.out", "bar.b.c");
-    buildShouldSucceed();
-  });
 }