Added shadow_dom polyfill to make the app run in other browsers

Author: pavelgj

Chapter_07/pubspec.yaml

@@ -4,5 +4,6 @@ dependencies:
   angular: any
   browser: any
   js: any
+  shadow_dom: any
 dev_dependencies:
   unittest: any

Chapter_07/web/index.html

@@ -9,5 +9,6 @@
 
   <script type="application/dart" src="main.dart"></script>
   <script type="text/javascript" src="packages/browser/dart.js"></script>
+  <script src="packages/shadow_dom/shadow_dom.debug.js"></script>
 </body>
 </html>