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

sdk/lib/_internal/pub_generated/test/run/app_can_read_from_stdin_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.
-
-import '../descriptor.dart' as d;
-import '../test_pub.dart';
-
-const SCRIPT = """
-import 'dart:io';
-
-main() {
-  print("started");
-  var line1 = stdin.readLineSync();
-  print("between");
-  var line2 = stdin.readLineSync();
-  print(line1);
-  print(line2);
-}
-""";
-
-main() {
-  initConfig();
-  integration('the spawned application can read from stdin', () {
-    d.dir(
-        appPath,
-        [d.appPubspec(), d.dir("bin", [d.file("script.dart", SCRIPT)])]).create();
-
-    var pub = pubRun(args: ["script"]);
-
-    pub.stdout.expect("started");
-    pub.writeLine("first");
-    pub.stdout.expect("between");
-    pub.writeLine("second");
-    pub.stdout.expect("first");
-    pub.stdout.expect("second");
-    pub.shouldExit(0);
-  });
-}