Revert commits r33138, r33135, and r33134.

pkg/barback/test/package_graph/errors_test.dart

Index: pkg/barback/test/package_graph/errors_test.dart
diff --git a/pkg/barback/test/package_graph/errors_test.dart b/pkg/barback/test/package_graph/errors_test.dart
index 24281784308c4a28c889add7d8d87d59f2d9f21b..8c74991309f451fed7b20cadc0fadbf0d584278a 100644
--- a/pkg/barback/test/package_graph/errors_test.dart
+++ b/pkg/barback/test/package_graph/errors_test.dart
@@ -114,6 +114,15 @@ main() {
     buildShouldFail([isTransformerException(equals(BadTransformer.ERROR))]);
   });
 
+  test("doesn't yield a source if a transform fails on it", () {
+    initGraph(["app|foo.txt"], {"app": [
+      [new BadTransformer(["app|foo.txt"])]
+    ]});
+
+    updateSources(["app|foo.txt"]);
+    expectNoAsset("app|foo.txt");
+  });
+
   test("catches errors even if nothing is waiting for process results", () {
     initGraph(["app|foo.txt"], {"app": [[new BadTransformer([])]]});