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

pkg/polymer/test/mirror_loader_4.dart

Index: pkg/polymer/test/mirror_loader_4.dart
diff --git a/pkg/polymer/test/mirror_loader_4.dart b/pkg/polymer/test/mirror_loader_4.dart
new file mode 100644
index 0000000000000000000000000000000000000000..7d882af816190baebb0e9e2e2514bd7601283d43
--- /dev/null
+++ b/pkg/polymer/test/mirror_loader_4.dart
@@ -0,0 +1,21 @@
+library mirror_loader_test4;
+
+import 'dart:html';
+import 'package:polymer/polymer.dart';
+
+@CustomTag('x-a')
+class XA extends PolymerElement {
+  final String x = "a";
+  XA.created() : super.created();
+}
+
+// The next classes are here as a regression test for darbug.com/17929. Our
+// loader was incorrectly trying to retrieve the reflectiveType of these
+// classes.
+class Foo<T> {}
+
+@CustomTag('x-b')
+class XB<T> extends PolymerElement {
+  final String x = "a";
+  XB.created() : super.created();
+}