anchor.diff:  
     List<String> _constructReproducingCommandArguments(Map config) {
       var arguments = new List<String>();
  -    for (var configKey in config.keys) {
  -      if (!_blacklistedOptions.contains(configKey)) {
  -        for (var option in _options) {
  -          var configValue = config[configKey];
  -          // We only include entries of [conf] if we find an option for it.
  -          if (configKey == option.name && configValue != option.defaultValue) {
  -            var isBooleanOption = option.type == 'bool';
  -            // Sort by length, so we get the shortest variant.
  -            var possibleOptions = new List.from(option.keys);
  -            possibleOptions.sort((a, b) => (a.length < b.length ? -1 : 1));
  -            var key = possibleOptions[0];
  -            if (key.startsWith('--')) {
  -              // long version
  -              arguments.add(key);
  -              if (!isBooleanOption) {
  -                arguments.add("$configValue");
  -              }
  -            } else {
  -              // short version
  -              assert(key.startsWith('-'));
  -              if (!isBooleanOption) {
  -                arguments.add("$key$configValue");
  -              } else {
  -                arguments.add(key);
  -              }
  -            }
  -          }
  -        }
  +    for (var option in _options) {
  +      var name = option.name;
  +      if (!config.containsKey(name) || _blacklistedOptions.contains(name)) {
  +        continue;
  +      }
  +      var value = config[name];
  +      if (config[name] == option.defaultValue ||
  +          (name == 'packages' &&
  +              value ==
  +                  TestUtils.dartDirUri.resolve('.packages').toFilePath())) {
  +        continue;
  +      }
  +      shortest(String a, String b) => a.length <= b.length ? a : b;
  +      var key = option.keys.reduce(shortest);
  +      if (option.type == 'bool') {
  +        arguments.add(key);
  +      } else if (key.startsWith('--')) {
  +        // long version
  +        arguments.add(key);
  +        arguments.add("$value");
  +      } else {
  +        // short version
  +        assert(key.startsWith('-'));
  +        arguments.add("$key$value");
         }
       }
       return arguments;
  
positive.code:           'noopt', 'Run an in-place precompilation', ['--noopt'], [], false,
            type: 'bool'),
        new _TestOptionSpecification(
            'fast_startup', 'Pass the --fast-startup flag to dart2js',
            ['--fast-startup'], [], false,
            type: 'bool'),
        new _TestOptionSpecification(
            'hot_reload', 'Run hot reload stress tests', ['--hot-reload'], [],
            false, type: 'bool'),
        new _TestOptionSpecification(
            'hot_reload_rollback',
            'Run hot reload rollback stress tests', ['--hot-reload-rollback'],
            [],
            false, type: 'bool'),
        new _TestOptionSpecification(
            'use_blobs',
            'Use mmap instead of shared libraries for precompilation',
            ['--use-blobs'], [], false, type: 'bool'),
        new _TestOptionSpecification(
            'timeout', 'Timeout in seconds', ['-t', '--timeout'], [], -1,
            type: 'int'),
  
negative.code:     if (configuration['package_root'] == null &&
          configuration['packages'] == null) {
        configuration['packages'] =
            TestUtils.dartDirUri.resolve('.packages').toFilePath();
      }
  
      // Expand the architectures.
  