add basic constructor that doesn't take BarbackSettings

test/transformer_test.dart

Index: test/transformer_test.dart
diff --git a/test/transformer_test.dart b/test/transformer_test.dart
index 3ef1ef66e1b5de1487e75de2efde6c9cda1e2c87..b27069a5423e34a12176bdc8a1f05733946cc532 100644
--- a/test/transformer_test.dart
+++ b/test/transformer_test.dart
@@ -4,15 +4,14 @@
 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': '''