Practically remove boot.js, adds the initialization from the Dart side of

pkg/polymer/test/instance_attrs_test.dart

Index: pkg/polymer/test/instance_attrs_test.dart
diff --git a/pkg/polymer/test/instance_attrs_test.dart b/pkg/polymer/test/instance_attrs_test.dart
index 71030797992954669cf2591aa5375da681031c35..45508bc153024a7e3a2c781ff0c77d66277ae6b1 100644
--- a/pkg/polymer/test/instance_attrs_test.dart
+++ b/pkg/polymer/test/instance_attrs_test.dart
@@ -11,9 +11,13 @@ import 'package:polymer/polymer.dart';
 @CustomTag('my-element')
 class MyElement extends PolymerElement {
   MyElement.created() : super.created();
+
+  // This is here so that [attributes] can be read via mirrors in polymer
+  // expressions (@CustomTag in this class makes the attribute reflectable).
+  get attributes => super.attributes;
 }
 
-main() {
+@initMethod _main() {
   useHtmlConfiguration();
 
   test('attributes were deserialized', () {