Use Directory.systemTemp getter in pkg subdirectory of repository.

pkg/analyzer_experimental/test/utils.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 utils;
 
 import 'dart:io';
 
 import 'package:analyzer_experimental/analyzer.dart';
 import 'package:path/path.dart' as pathos;
@@ skipping 20 matching lines @@
     }
     return null;
   });
 }
 
 /// Creates a temporary directory and passes its path to [fn]. Once [fn]
 /// completes, the temporary directory and all its contents will be deleted.
 ///
 /// Returns the return value of [fn].
 dynamic withTempDir(fn(String path)) {
-  var tempDir = new Directory('').createTempSync().path;
+  var tempDir =
+      Directory.systemTemp.createTempSync('analyzer_experimental_').path;
   try {
     return fn(tempDir);
   } finally {
     new Directory(tempDir).deleteSync(recursive: true);
   }
 }