Revert "Revert "Use native async/await support in pub.""

sdk/lib/_internal/pub_generated/test/serve/unknown_dependency_test.dart

Index: sdk/lib/_internal/pub_generated/test/serve/unknown_dependency_test.dart
diff --git a/sdk/lib/_internal/pub_generated/test/serve/unknown_dependency_test.dart b/sdk/lib/_internal/pub_generated/test/serve/unknown_dependency_test.dart
deleted file mode 100644
index daa3c440ba984e59a76d346a9f94997eb655bda1..0000000000000000000000000000000000000000
--- a/sdk/lib/_internal/pub_generated/test/serve/unknown_dependency_test.dart
+++ /dev/null
@@ -1,23 +0,0 @@
-// 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 '../descriptor.dart' as d;
-import '../test_pub.dart';
-import 'utils.dart';
-
-main() {
-  initConfig();
-  integration("responds with a 404 unknown dependencies", () {
-    d.dir(appPath, [d.appPubspec()]).create();
-
-    pubServe();
-    requestShould404("packages/foo/nope.dart");
-    requestShould404("assets/foo/nope.png");
-    requestShould404("dir/packages/foo/nope.dart");
-    requestShould404("dir/assets/foo/nope.png");
-    endPubServe();
-  });
-}