Use browser_controller instead of selenium in test scripts, by default.

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 "dart:math";
 import "drt_updater.dart";
 import "test_suite.dart";
@@ skipping 288 matching lines @@
               ['--write-debug-log'],
               [],
               false,
               'bool'
               ),
           new _TestOptionSpecification(
               'use_browser_controller',
               'Use the new selenium replacement browser-controller.',
               ['--use_browser_controller'],
               [],
-              false,
+              true,
               'bool'
               ),
           new _TestOptionSpecification(
               'clear_safari_cache',
               'Clear the safari cache (i.e., delete it).',
               ['--clear_safari_cache'],
               [],
               false,
               'bool'
               ),
@@ skipping 478 matching lines @@
         return option;
       }
     }
     print('Unknown test option $name');
     exit(1);
   }
 
 
   List<_TestOptionSpecification> _options;
 }