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

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

-// 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("'packages' URLs look in the app's lib directory", () {
-    d.dir(
-        appPath,
-        [
-            d.appPubspec(),
-            d.dir(
-                "lib",
-                [
-                    d.file("lib.dart", "foo() => 'foo';"),
-                    d.dir("sub", [d.file("lib.dart", "bar() => 'bar';"),])])]).create();
-
-    pubServe();
-    requestShouldSucceed("packages/myapp/lib.dart", "foo() => 'foo';");
-    requestShouldSucceed("packages/myapp/sub/lib.dart", "bar() => 'bar';");
-
-    // "packages" can be in a subpath of the URL:
-    requestShouldSucceed("foo/packages/myapp/lib.dart", "foo() => 'foo';");
-    requestShouldSucceed("a/b/packages/myapp/sub/lib.dart", "bar() => 'bar';");
-    endPubServe();
-  });
-}