Replace bootstrap logic with 'boot.js', use 'component/dart' mime-type and add

pkg/polymer/test/publish_attributes_test.dart

Index: pkg/polymer/test/publish_attributes_test.dart
diff --git a/pkg/polymer/test/publish_attributes_test.dart b/pkg/polymer/test/publish_attributes_test.dart
index 33966e744f404df4c9f458f673fc896eafc6c84d..d4ecdded2fa4f6b30debf7fb8237308656a47a61 100644
--- a/pkg/polymer/test/publish_attributes_test.dart
+++ b/pkg/polymer/test/publish_attributes_test.dart
@@ -52,8 +52,8 @@ class XQux extends XBaz {
   XQux.created() : super.created();
 }
 
+@initMethod
 main() {
-  initPolymer();
   useHtmlConfiguration();
 
   setUp(() => Polymer.onReady);