Put tree-shaking behind a flag in dartk.

tools/testing/dart/test_options.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 test_options_parser;
 
 import "dart:io";
 import "drt_updater.dart";
 import "test_suite.dart";
 import "path.dart";
@@ skipping 273 matching lines @@
       new _TestOptionSpecification(
           'help', 'Print list of options', ['-h', '--help'], [], false,
           type: 'bool'),
       new _TestOptionSpecification(
           'verbose', 'Verbose output', ['-v', '--verbose'], [], false,
           type: 'bool'),
       new _TestOptionSpecification(
           'verify-ir', 'Verify kernel IR', ['--verify-ir'], [], false,
           type: 'bool'),
       new _TestOptionSpecification(
+          'no-tree-shake', 'Disable kernel IR tree shaking', ['--no-tree-shake'], [], false,
+          type: 'bool'),
+      new _TestOptionSpecification(
           'use-standalone-dartk', 'Generate Kernel binaries with a standalone dartk compiler', ['--use-standalone-dartk'], [], false,
           type: 'bool'),
       new _TestOptionSpecification(
           'list', 'List tests only, do not run them', ['--list'], [], false,
           type: 'bool'),
       new _TestOptionSpecification(
           'report_in_json',
           'When doing list, output result summary in json only.',
           ['--report-in-json'],
           [],
@@ skipping 712 matching lines @@
         return option;
       }
     }
     print('Unknown test option $name');
     exit(1);
     return null; // Unreachable.
   }
 
   List<_TestOptionSpecification> _options;
 }