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

pkg/polymer/test/register_test.dart

Index: pkg/polymer/test/register_test.dart
diff --git a/pkg/polymer/test/register_test.dart b/pkg/polymer/test/register_test.dart
index 8afb734d2b63d93bd58375ad3d1caee9fe3c72d5..f5f2bda89014da5bbc924db49ced9881340a1569 100644
--- a/pkg/polymer/test/register_test.dart
+++ b/pkg/polymer/test/register_test.dart
@@ -27,8 +27,8 @@ class XDiv2Element extends XDivElement {
   XDiv2Element.created() : super.created();
 }
 
+@initMethod
 main() {
-  initPolymer();
   useHtmlConfiguration();
 
   setUp(() => Polymer.onReady);