anchor.diff:    Playground() {
       sourceTabController = new TabController();
       for (String name in ['dart', 'html', 'css']) {
  -      sourceTabController.registerTab(new TabElement(
  -          querySelector('#${name}tab'), name: name, onSelect: () {
  -            Element issuesElement = querySelector('#issues');
  -            issuesElement.style.display = name == 'dart' ? 'block' : 'none';
  -            ga.sendEvent('edit', name);
  -            _context.switchTo(name);
  -          }));
  +      sourceTabController.registerTab(
  +          new TabElement(querySelector('#${name}tab'), name: name,
  +              onSelect: () {
  +        Element issuesElement = querySelector('#issues');
  +        issuesElement.style.display = name == 'dart' ? 'block' : 'none';
  +        ga.sendEvent('edit', name);
  +        _context.switchTo(name);
  +      }));
       }
   
       overlay = new DOverlay(querySelector('#frame_overlay'));
  
positive.code:         editableGist.setBackingGist(blankGist);
        });
      } else if (url.hasQuery && url.queryParameters['source'] != null) {
        dartSupportServices.retrieveGist(id: url.queryParameters['source']).then((UuidContainer gistId) {
          gistLoader.loadGist(gistId.uuid).then((Gist backing) {
            editableGist.setBackingGist(backing);
            router.go('gist', {'gist': ''});
  
negative.code: 
    Future shareAnon({String summary: ""}) {
      return gistLoader
          .createAnon(mutableGist.createGist(summary: summary))
          .then((Gist newGist) {
        editableGist.setBackingGist(newGist);
        overrideNextRoute(newGist);
        router.go('gist', {'gist': newGist.id});
  