Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/snapshot/updates_snapshot_for_git_dependency_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("upgrades a snapshot when a git dependency is upgraded", () {
-    ensureGit();
-
-    d.git('foo.git', [d.pubspec({
-        "name": "foo",
-        "version": "0.0.1"
-      }),
-          d.dir(
-              "bin",
-              [d.file("hello.dart", "void main() => print('Hello!');")])]).create();
-
-    d.appDir({
-      "foo": {
-        "git": "../foo.git"
-      }
-    }).create();
-
-    pubGet(output: contains("Precompiled foo:hello."));
-
-    d.dir(
-        p.join(appPath, '.pub', 'bin', 'foo'),
-        [d.matcherFile('hello.dart.snapshot', contains('Hello!'))]).validate();
-
-    d.git(
-        'foo.git',
-        [
-            d.dir(
-                "bin",
-                [d.file("hello.dart", "void main() => print('Goodbye!');")])]).commit();
-
-    pubUpgrade(output: contains("Precompiled foo:hello."));
-
-    d.dir(
-        p.join(appPath, '.pub', 'bin', 'foo'),
-        [d.matcherFile('hello.dart.snapshot', contains('Goodbye!'))]).validate();
-
-    var process = pubRun(args: ['foo:hello']);
-    process.stdout.expect("Goodbye!");
-    process.shouldExit();
-  });
-}