Bring back initPolymer, allow boot.js only if using "polymer_experimental.html".

pkg/polymer/test/nested_binding_test.dart

Index: pkg/polymer/test/nested_binding_test.dart
diff --git a/pkg/polymer/test/nested_binding_test.dart b/pkg/polymer/test/nested_binding_test.dart
index cdc36147d467446c3986b36ba30653e498c7878a..c6ab7ef32c021dea4e6836f734f84ee74e97081a 100644
--- a/pkg/polymer/test/nested_binding_test.dart
+++ b/pkg/polymer/test/nested_binding_test.dart
@@ -28,12 +28,11 @@ class MyTest extends PolymerElement {
   }
 }
 
-@initMethod
-main() {
+main() => initPolymer().run(() {
   useHtmlConfiguration();
 
   setUp(() => Polymer.onReady);
 
   test('ready called',
       () => (querySelector('my-test') as MyTest)._testDone.future);
-}
+});