Support loading transformer plugins from pub.

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

Index: sdk/lib/_internal/pub/test/serve/fails_to_load_a_transform_with_an_import_error_test.dart
diff --git a/sdk/lib/_internal/pub/test/serve/fails_to_load_a_transform_with_an_import_error_test.dart b/sdk/lib/_internal/pub/test/serve/fails_to_load_a_transform_with_an_import_error_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..f663af0f586e02e73dfa247994e52641f2992a65
--- /dev/null
+++ b/sdk/lib/_internal/pub/test/serve/fails_to_load_a_transform_with_an_import_error_test.dart
@@ -0,0 +1,35 @@
+// 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();
+
+  // An import error will cause the isolate API to fail synchronously while
+  // loading the transformer.
+  integration("fails to load a transform with an import error", () {
+    d.dir(appPath, [
+      d.pubspec({
+        "name": "myapp",
+        "transformers": ["myapp/src/transformer"]
+      }),
+      d.dir("lib", [d.dir("src", [
+        d.file("transformer.dart", "import 'does/not/exist.dart';")
+      ])])
+    ]).create();
+
+    createLockFile('myapp', {}, pkg: ['barback']);
+
+    var pub = startPub(args: ['serve', '--port=0']);
+    expect(pub.nextErrLine(), completion(matches(new RegExp(
+        r"Error: line 1 pos 1: library handler failed$"))));
+    pub.shouldExit(1);
+  });
+}