Bring back initPolymer, allow boot.js only if using "polymer_experimental.html".

samples/searchable_list/test/demo_app_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library todomvc.test.markdone_test;
 
 import 'dart:async';
 import 'dart:html';
 import 'package:polymer/polymer.dart';
 import 'package:unittest/unittest.dart';
 import 'package:unittest/html_config.dart';
 import '../web/elements/demo_app.dart';
 
 /**
  * A trivial test to get the analyzer plugged into this sample. See
  * searchable_list_test.dart.
  */
-@initMethod
 main() {
+  initPolymer();
   useHtmlConfiguration();
 
   setUp(() => Polymer.onReady);
 
   test('loading the element', () {
     return new Future(() {
       var demoApp = querySelector('demo-app');
       expect(demoApp is DemoApp, isTrue);
     });
   });
 }