Use native async/await support in pub.

sdk/lib/_internal/pub/test/async_compile_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 'dart:io';
-
-import 'package:path/path.dart' as p;
-import 'package:scheduled_test/descriptor.dart' as d;
-import 'package:scheduled_test/scheduled_test.dart';
-import 'package:scheduled_test/scheduled_process.dart';
-
-import 'test_pub.dart';
-import '../lib/src/io.dart';
-
-void main() {
-  integration("the generated pub source is up to date", () {
-    var compilerArgs = Platform.executableArguments.toList()..addAll([
-      p.join(pubRoot, 'bin', 'async_compile.dart'),
-      '--force', '--verbose',
-      p.join(sandboxDir, "pub_generated")
-    ]);
-
-    new ScheduledProcess.start(Platform.executable, compilerArgs).shouldExit(0);
-
-    new d.DirectoryDescriptor.fromFilesystem("pub_generated",
-        p.join(pubRoot, "..", "pub_generated")).validate();
-  });
-}