Fix a bug in barback's static package handling.

pkg/barback/test/static_provider_test.dart

Index: pkg/barback/test/static_provider_test.dart
diff --git a/pkg/barback/test/static_provider_test.dart b/pkg/barback/test/static_provider_test.dart
index 08aad6f9b9cc9ba504bf3415c7b8d651339dadc3..4bd44f9972082d86e4ba0362a7a329a4562485a2 100644
--- a/pkg/barback/test/static_provider_test.dart
+++ b/pkg/barback/test/static_provider_test.dart
@@ -31,4 +31,10 @@ main() {
     updateSources(["app|a.txt"]);
     expectAsset("app|a.out", "b");
   });
+
+  test("can list all static assets", () {
+    initStaticGraph(["app|foo.txt", "app|bar.txt", "app|baz.txt"],
+        staticPackages: ["app"]);
+    expectAllAssets(["app|foo.txt", "app|bar.txt", "app|baz.txt"]);
+  });
 }