Update Dart binaries to 1.18.0-dev.4.4

tools/testing/dart/test_progress.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 test_progress;
 
 import "dart:async";
 import "dart:io";
 import "dart:io" as io;
 import "dart:convert" show JSON;
@@ skipping 446 matching lines @@
   static RegExp _getTemporaryDirectoryRegexp() {
     // These are the patterns of temporary directory names created by
     // 'Directory.systemTemp.createTemp()' on linux/macos and windows.
     if (['macos', 'linux'].contains(Platform.operatingSystem)) {
       return new RegExp(r'^temp_dir1_......$');
     } else {
       return new RegExp(r'tempdir-........-....-....-....-............$');
     }
   }
 
-  static Stream<Directory> getLeftOverTemporaryDirectories() {
+  static Stream<FileSystemEntity> getLeftOverTemporaryDirectories() {
     var regExp = _getTemporaryDirectoryRegexp();
     return Directory.systemTemp.list().where(
         (FileSystemEntity fse) {
           if (fse is Directory) {
             if (regExp.hasMatch(new Path(fse.path).filename)) {
               return true;
             }
           }
           return false;
         });
@@ skipping 198 matching lines @@
       return new VerboseProgressIndicator(startTime);
     case 'status':
       return new ProgressIndicator(startTime);
     case 'buildbot':
       return new BuildbotProgressIndicator(startTime);
     default:
       assert(false);
       break;
   }
 }