Store the async-await compiled pub code directly in the repo.

sdk/lib/_internal/pub_generated/test/serve/404_page_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 'package:scheduled_test/scheduled_test.dart';
-
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 import 'utils.dart';
-
 main() {
   initConfig();
   setUp(() {
-    d.dir(appPath, [
-      d.appPubspec()
-    ]).create();
+    d.dir(appPath, [d.appPubspec()]).create();
   });
-
   integration("the 404 page describes the missing asset", () {
     pubServe();
-
     scheduleRequest("packages/foo/missing.txt").then((response) {
       expect(response.statusCode, equals(404));
-
-      // Should mention the asset that can't be found.
       expect(response.body, contains("foo"));
       expect(response.body, contains("missing.txt"));
     });
-
     endPubServe();
   });
-
   integration("the 404 page describes the error", () {
     pubServe();
-
     scheduleRequest("packages").then((response) {
       expect(response.statusCode, equals(404));
-
-      // Should mention the asset that can't be found.
       expect(response.body, contains('"/packages"'));
     });
-
     endPubServe();
   });
 }