Add temporary directory for dartc compilation of tests.

tools/testing/dart/test_options.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_options_parser");
 
 List<String> defaultTestSelectors =
     const ['dartc', 'samples', 'standalone', 'corelib', 'co19', 'language',
            'isolate', 'stub-generator', 'vm', 'client', 'dartdoc'];
 
@@ skipping 114 matching lines @@
               false,
               'bool'),
           new _TestOptionSpecification(
               'list',
               'List tests only, do not run them',
               ['--list'],
               [],
               false,
               'bool'),
           new _TestOptionSpecification(
+              'keep-generated-tests',
+              'Keep the generated files in the temporary directory',
+              ['--keep-generated-tests'],
+              [],
+              false,
+              'bool'),
+          new _TestOptionSpecification(
               'valgrind',
               'Run tests through valgrind',
               ['--valgrind'],
               [],
               false,
               'bool'),
           new _TestOptionSpecification(
               'special-command',
               specialCommandHelp,
               ['--special-command'],
@@ skipping 326 matching lines @@
         return option;
       }
     }
     print('Unknown test option $name');
     exit(1);
   }
 
 
   List<_TestOptionSpecification> _options;
 }