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

sdk/lib/_internal/pub_generated/test/run/allows_dart_extension_test.dart

Index: sdk/lib/_internal/pub_generated/test/run/allows_dart_extension_test.dart
diff --git a/sdk/lib/_internal/pub_generated/test/run/allows_dart_extension_test.dart b/sdk/lib/_internal/pub_generated/test/run/allows_dart_extension_test.dart
deleted file mode 100644
index 90d1d8a6547307eda58cbb47dd7f528ee256855c..0000000000000000000000000000000000000000
--- a/sdk/lib/_internal/pub_generated/test/run/allows_dart_extension_test.dart
+++ /dev/null
@@ -1,30 +0,0 @@
-// 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() {
-  stdout.writeln("stdout output");
-  stderr.writeln("stderr output");
-  exitCode = 123;
-}
-""";
-
-main() {
-  initConfig();
-  integration('allows a ".dart" extension on the argument', () {
-    d.dir(
-        appPath,
-        [d.appPubspec(), d.dir("bin", [d.file("script.dart", SCRIPT)])]).create();
-
-    var pub = pubRun(args: ["script.dart"]);
-    pub.stdout.expect("stdout output");
-    pub.stderr.expect("stderr output");
-    pub.shouldExit(123);
-  });
-}