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

pkg/polymer/test/mirror_loader_1.dart

Index: pkg/polymer/test/mirror_loader_1.dart
diff --git a/pkg/polymer/test/mirror_loader_1.dart b/pkg/polymer/test/mirror_loader_1.dart
new file mode 100644
index 0000000000000000000000000000000000000000..4fbe74a2a6b44b5a9510236bd6c5d4f96e222e46
--- /dev/null
+++ b/pkg/polymer/test/mirror_loader_1.dart
@@ -0,0 +1,10 @@
+library mirror_loader_test1;
+
+import 'dart:html';
+import 'package:polymer/polymer.dart';
+
+@CustomTag('x-a')
+class XA extends PolymerElement {
+  final String x = "a";
+  XA.created() : super.created();
+}