add basic constructor that doesn't take BarbackSettings

test/transformer_test.dart

 // Copyright (c) 2015, 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 initialize.transformer_test;
 
 import 'common.dart';
-import 'package:barback/barback.dart';
 import 'package:initialize/transformer.dart';
 import 'package:unittest/compact_vm_config.dart';
 
 main() {
   useCompactVMConfiguration();
 
-  var transformer = new InitializeTransformer.asPlugin(
-      new BarbackSettings({'entryPoint': 'web/index.dart'}, BarbackMode.DEBUG));
+  var transformer =
+      new InitializeTransformer('web/index.dart', 'web/index.bootstrap.dart');
 
   testPhases('transformer', [[transformer]], {
     'a|web/index.dart': '''
           library web_foo;
 
           import 'foo.dart';
           ''',
     'a|web/foo.dart': '''
           @constInit
           library foo;
@@ skipping 62 matching lines @@
               new InitEntry(i2.constInit, #foo),
               new InitEntry(i2.initMethod, i3.foo),
               new InitEntry(i2.constInit, i3.Foo),
             ]);
 
             i0.main();
           }
           '''.replaceAll('          ', '')
   });
 }