Fix test.dart multitest generated_test directory on Windows.

tools/testing/dart/test_suite.dart

 // Copyright (c) 2011, 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_suite");
 
 #import("status_file_parser.dart");
 #import("test_runner.dart");
 #import("multitest.dart");
 
@@ skipping 315 matching lines @@
     RegExp pattern = configuration['selectors'][suiteName];
     if (!pattern.hasMatch(filename)) return;
     if (filename.endsWith('test_config.dart')) return;
 
     var optionsFromFile = optionsFromFile(filename);
     Function createTestCase = makeTestCaseCreator(optionsFromFile);
 
     if (optionsFromFile['isMultitest']) {
       testGeneratorStarted();
       DoMultitest(filename,
-                  TestUtils.outputDir(configuration),
+                  TestUtils.buildDir(configuration),
                   directoryPath,
                   createTestCase,
                   testGeneratorDone);
     } else {
       createTestCase(filename, optionsFromFile['isNegative']);
     }
   }
 
   void enqueueBrowserTest(String filename,
                           String testName,
@@ skipping 671 matching lines @@
  * $noCrash tests are expected to be flaky but not crash
  * $pass tests are expected to pass
  * $failOk tests are expected to fail that we won't fix
  * $fail tests are expected to fail that we should fix
  * $crash tests are expected to crash that we should fix
  * $timeout tests are allowed to timeout
 """;
     print(report);
    }
 }