Use native async/await support in pub.

sdk/lib/_internal/pub_generated/test/descriptor/tar.dart

-// Copyright (c) 2013, 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 descriptor.tar;
-
-import 'dart:async';
-
-import 'package:path/path.dart' as path;
-import 'package:scheduled_test/scheduled_test.dart';
-import 'package:scheduled_test/descriptor.dart';
-
-import '../../lib/src/io.dart';
-
-/// Describes a tar file and its contents.
-class TarFileDescriptor extends DirectoryDescriptor implements
-    ReadableDescriptor {
-  TarFileDescriptor(String name, List<Descriptor> contents)
-      : super(name, contents);
-
-  /// Creates the files and directories within this tar file, then archives
-  /// them, compresses them, and saves the result to [parentDir].
-  Future<String> create([String parent]) => schedule(() {
-    if (parent == null) parent = defaultRoot;
-    return withTempDir((tempDir) {
-      return Future.wait(contents.map((entry) {
-        return entry.create(tempDir);
-      })).then((_) {
-        var createdContents =
-            listDir(tempDir, recursive: true, includeHidden: true);
-        return createTarGz(createdContents, baseDir: tempDir).toBytes();
-      }).then((bytes) {
-        var file = path.join(parent, name);
-        writeBinaryFile(file, bytes);
-        return file;
-      });
-    });
-  }, 'creating tar file:\n${describe()}');
-
-  /// Validates that the `.tar.gz` file at [path] contains the expected
-  /// contents.
-  Future validate([String parent]) {
-    throw new UnimplementedError("TODO(nweiz): implement this");
-  }
-
-  Stream<List<int>> read() {
-    return new Stream<List<int>>.fromFuture(withTempDir((tempDir) {
-      return create(
-          tempDir).then((_) => readBinaryFile(path.join(tempDir, name)));
-    }));
-  }
-}