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

utils/tests/pub/test_pub.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.
 
 /**
  * Test infrastructure for testing pub. Unlike typical unit tests, most pub
  * tests are integration tests that stage some stuff on the file system, run
  * pub, and then validate the results. This library provides an API to build
  * tests like that.
  */
@@ skipping 298 matching lines @@
       if (!installed &&
           !Platform.environment.containsKey('BUILDBOT_BUILDERNAME')) {
         _abortScheduled = true;
       }
       return null;
     });
   });
 }
 
 Future<Directory> _setUpSandbox() {
-  return createTempDir('pub-test-sandbox-');
+  return createTempDir();
 }
 
 Future _runScheduled(Directory parentDir, List<_ScheduledEvent> scheduled) {
   if (scheduled == null) return new Future.immediate(null);
   var iterator = scheduled.iterator();
 
   Future runNextEvent([_]) {
     if (_abortScheduled || !iterator.hasNext()) {
       _abortScheduled = false;
       scheduled.clear();
@@ skipping 453 matching lines @@
    */
   InputStream load(List<String> path) {
     if (!path.isEmpty()) {
       var joinedPath = Strings.join(path, '/');
       throw "Can't load $joinedPath from within $name: not a directory.";
     }
 
     var sinkStream = new ListInputStream();
     var tempDir;
     // TODO(nweiz): propagate any errors to the return value. See issue 3657.
-    createTempDir("pub-test-tmp-").chain((_tempDir) {
+    createTempDir().chain((_tempDir) {
       tempDir = _tempDir;
       return create(tempDir);
     }).then((tar) {
       var sourceStream = tar.openInputStream();
       pipeInputToInput(
           sourceStream, sinkStream, onClosed: tempDir.deleteRecursively);
     });
     return sinkStream;
   }
 }
 
 /**
  * Schedules a callback to be called as part of the test case.
  */
 void _schedule(_ScheduledEvent event) {
   if (_scheduled == null) _scheduled = [];
   _scheduled.add(event);
 }
 
 /**
  * Schedules a callback to be called after Pub is run with [runPub], even if it
  * fails.
  */
 void _scheduleCleanup(_ScheduledEvent event) {
   if (_scheduledCleanup == null) _scheduledCleanup = [];
   _scheduledCleanup.add(event);
 }