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

pkg/polymer/test/prop_attr_reflection_test.dart

Index: pkg/polymer/test/prop_attr_reflection_test.dart
diff --git a/pkg/polymer/test/prop_attr_reflection_test.dart b/pkg/polymer/test/prop_attr_reflection_test.dart
index a0dbf51641e7eb7b6c114a0f98116f81cb53361a..927ebabd0214a84dd9bf13621f770ce15ef3f637 100644
--- a/pkg/polymer/test/prop_attr_reflection_test.dart
+++ b/pkg/polymer/test/prop_attr_reflection_test.dart
@@ -40,8 +40,8 @@ Future onAttributeChange(Element node) {
   return completer.future;
 }
 
+@initMethod
 main() {
-  initPolymer();
   useHtmlConfiguration();
 
   setUp(() => Polymer.onReady);