Enable cross-package transforms to see new transformers in other packages.

pkg/barback/test/package_graph/add_remove_transform_test.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.package_graph.transform_test;
 
 import 'package:barback/src/utils.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../utils.dart';
@@ skipping 173 matching lines @@
     updateTransformers("app", [
       [rewrite],
       [new RewriteTransformer("blub", "blab")]
     ]);
     expectAsset("app|foo.blab", "foo.blab");
     expectNoAsset("app|foo.blub");
     buildShouldSucceed();
   });
 
   test("a cross-package transform sees a new transformer in a new phase", () {
-    // TODO(nweiz): make this work.
-    return;
-
     var rewrite = new RewriteTransformer("inc", "inc");
     initGraph({
       "pkg1|foo.txt": "pkg2|foo.inc",
       "pkg2|foo.inc": "foo"
     }, {
       "pkg1": [[new ManyToOneTransformer("txt")]],
       "pkg2": [[rewrite]]
     });
 
     updateSources(["pkg1|foo.txt", "pkg2|foo.inc"]);
-    expectAsset("pkg1|foo.out", "foo");
+    expectAsset("pkg1|foo.out", "foo.inc");
     buildShouldSucceed();
 
     updateTransformers("pkg2", [
       [rewrite],
       [new RewriteTransformer("inc", "inc")]
     ]);
     expectAsset("pkg1|foo.out", "foo.inc.inc");
     buildShouldSucceed();
   });
 
@@ skipping 13 matching lines @@
 
     updateSources(["pkg1|foo.txt", "pkg2|foo.inc"]);
     expectAsset("pkg1|foo.out", "foo.inc.inc");
     buildShouldSucceed();
 
     updateTransformers("pkg2", [[rewrite]]);
     expectAsset("pkg1|foo.out", "foo.inc");
     buildShouldSucceed();
   });
 }