Don't pollute repo with temp dirs for pub tests.

utils/pub/io.dart

 // Copyright (c) 2012, 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.
 
 /**
  * Helper functionality to make working with IO easier.
  */
 #library('io');
 
 #import('dart:io');
@@ skipping 154 matching lines @@
         return true;
       });
       future.then(completer.complete);
       return completer.future;
     });
   });
 }
 
 /**
  * Creates a temp directory whose name will be based on [dir] with a unique
- * suffix appended to it. Returns a [Future] that completes when the directory
- * is created.
+ * suffix appended to it. If [dir] is not provided, a temp directory will be
+ * created in a platform-dependent temporary location. Returns a [Future] that
+ * completes when the directory is created.
  */
-Future<Directory> createTempDir(dir) {
+Future<Directory> createTempDir([dir = '']) {
   dir = _getDirectory(dir);
   return dir.createTemp();
 }
 
 /**
  * Asynchronously recursively deletes [dir], which can be a [String] or a
  * [Directory]. Returns a [Future] that completes when the deletion is done.
  */
 Future<Directory> deleteDir(dir) {
   dir = _getDirectory(dir);
@@ skipping 294 matching lines @@
   return new Directory(entry);
 }
 
 /**
  * Gets a [Uri] for [uri], which can either already be one, or be a [String].
  */
 Uri _getUri(uri) {
   if (uri is Uri) return uri;
   return new Uri.fromString(uri);
 }