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

pkg/polymer/test/js_interop_test.dart

Index: pkg/polymer/test/js_interop_test.dart
diff --git a/pkg/polymer/test/js_interop_test.dart b/pkg/polymer/test/js_interop_test.dart
index 3704ccb93addc5a6d30b535d2459d6cb484bd6bf..fc6f41c89507f574fbf8604a08705ba92d4562e9 100644
--- a/pkg/polymer/test/js_interop_test.dart
+++ b/pkg/polymer/test/js_interop_test.dart
@@ -16,7 +16,8 @@ class DartElement extends PolymerElement {
   DartElement.created() : super.created();
 }
 
-main() => initPolymer().run(() {
+@initMethod
+main() {
   useHtmlConfiguration();
 
   setUp(() => Polymer.onReady);
@@ -31,7 +32,7 @@ main() => initPolymer().run(() {
 
   test('js-element in dart-element', () => testInterop(
       querySelector('dart-element').shadowRoot.querySelector('js-element')));
-});
+}
 
 testInterop(jsElem) {
   expect(jsElem.shadowRoot.text, 'FOOBAR');