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

sdk/lib/_internal/pub_generated/test/snapshot/doesnt_resnapshot_when_a_dependency_is_unchanged_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(
-      "doesn't recreate a snapshot when no dependencies of a package " "have changed",
-      () {
-    servePackages((builder) {
-      builder.serve("foo", "1.2.3", deps: {
-        "bar": "any"
-      },
-          contents: [
-              d.dir("bin", [d.file("hello.dart", "void main() => print('hello!');")])]);
-      builder.serve("bar", "1.2.3");
-    });
-
-    d.appDir({
-      "foo": "1.2.3"
-    }).create();
-
-    pubGet(output: contains("Precompiled foo:hello."));
-
-    pubUpgrade(output: isNot(contains("Precompiled foo:hello.")));
-
-    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!'))])]).validate();
-  });
-}