Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/snapshot/creates_a_snapshot_test.dart

-// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS 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:path/path.dart' as p;
-import 'package:scheduled_test/scheduled_test.dart';
-
-import '../descriptor.dart' as d;
-import '../test_pub.dart';
-
-main() {
-  initConfig();
-  integration(
-      "creates a snapshot for an immediate dependency's executables",
-      () {
-    servePackages((builder) {
-      builder.serve(
-          "foo",
-          "1.2.3",
-          contents: [
-              d.dir(
-                  "bin",
-                  [
-                      d.file("hello.dart", "void main() => print('hello!');"),
-                      d.file("goodbye.dart", "void main() => print('goodbye!');"),
-                      d.file("shell.sh", "echo shell"),
-                      d.dir("subdir", [d.file("sub.dart", "void main() => print('sub!');")])])]);
-    });
-
-    d.appDir({
-      "foo": "1.2.3"
-    }).create();
-
-    pubGet(
-        output: allOf(
-            [contains("Precompiled foo:hello."), contains("Precompiled foo:goodbye.")]));
-
-    d.dir(
-        p.join(appPath, '.pub', 'bin'),
-        [
-            d.file('sdk-version', '0.1.2+3\n'),
-            d.dir(
-                'foo',
-                [
-                    d.matcherFile('hello.dart.snapshot', contains('hello!')),
-                    d.matcherFile('goodbye.dart.snapshot', contains('goodbye!')),
-                    d.nothing('shell.sh.snapshot'),
-                    d.nothing('subdir')])]).validate();
-
-    var process = pubRun(args: ['foo:hello']);
-    process.stdout.expect("hello!");
-    process.shouldExit();
-
-    process = pubRun(args: ['foo:goodbye']);
-    process.stdout.expect("goodbye!");
-    process.shouldExit();
-  });
-}