Support loading transformer plugins from pub.

sdk/lib/_internal/pub/test/serve/fails_to_load_a_transform_from_a_non_dependency_test.dart

Index: sdk/lib/_internal/pub/test/serve/fails_to_load_a_transform_from_a_non_dependency_test.dart
diff --git a/sdk/lib/_internal/pub/test/serve/fails_to_load_a_transform_from_a_non_dependency_test.dart b/sdk/lib/_internal/pub/test/serve/fails_to_load_a_transform_from_a_non_dependency_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..57c3349a15bccac1df15095acc7b9e1edb5392a6
--- /dev/null
+++ b/sdk/lib/_internal/pub/test/serve/fails_to_load_a_transform_from_a_non_dependency_test.dart
@@ -0,0 +1,29 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.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 pub_tests;
+
+import 'package:scheduled_test/scheduled_test.dart';
+
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+
+main() {
+  initConfig();
+  integration("fails to load a transform from a non-dependency", () {
+    d.dir(appPath, [
+      d.pubspec({
+        "name": "myapp",
+        "transformers": ["foo"]
+      })
+    ]).create();
+
+    var pub = startPub(args: ['serve', '--port=0']);
+    // Ignore the line containing the path to the pubspec.
+    expect(pub.nextErrLine(), completes);
+    expect(pub.nextErrLine(),
+        completion(equals('Could not find package for transformer "foo".')));
+    pub.shouldExit(1);
+  });
+}