add mutation observer polyfill package

pkg/custom_element/test/custom_element_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 custom_element.test.custom_element_test;
 
 import 'dart:async';
 import 'dart:html';
 import 'package:custom_element/custom_element.dart';
 import 'package:unittest/html_config.dart';
 import 'package:unittest/unittest.dart';
 
 main() {
   useHtmlConfiguration();
 
+  // Load the MutationObserver polyfill.
+  HttpRequest.getString('/root_dart/pkg/mutation_observer/lib/'
+      'mutation_observer.js').then((code) {
+    document.head.children.add(new ScriptElement()..text = code);

[blois, 2013/07/30 17:11:09]

Is this test run under CSP? If so, does it need an exclusion?

[Jennifer Messerly, 2013/07/30 18:05:20]

I think it will be okay because Chrome is the only browser we test in CSP and it
supports MutationObserver natively. I ran test.py locally with Chrome and CSP
and it seemed to work. If not I can update the status file.

+
+    customElementTests();
+  });
+}
+
+customElementTests() {
   test('register creates the element and calls lifecycle methods', () {
     // Add element to the page.
     var element = new Element.html('<fancy-button>foo bar</fancy-button>');
     document.body.nodes.add(element);
 
     var xtag = null;
     registerCustomElement('fancy-button', () => xtag = new FancyButton());
     expect(xtag, isNotNull, reason: 'FancyButton was created');
     expect(element.xtag, xtag, reason: 'xtag pointer should be set');
     expect(xtag.host, element, reason: 'host pointer should be set');
@@ skipping 45 matching lines @@
   }
   inserted() {
     super.inserted();
     lifecycle.add('inserted');
   }
   removed() {
     super.removed();
     lifecycle.add('removed');
   }
 }