first draft of polymer element tutorial

src/site/docs/tutorials/polymer-intro/examples/stopwatch/out/web/index.html_bootstrap.dart

+library app_bootstrap;
+
+import 'package:polymer/polymer.dart';
+import 'dart:mirrors' show currentMirrorSystem;
+
+import 'tute_stopwatch.dart' as i0;
+
+void main() {
+  initPolymer([
+      'tute_stopwatch.dart',
+    ], currentMirrorSystem().isolate.rootLibrary.uri.toString());
+}