anchor.diff:    }
   
     void _registerDesignerProxyListener() {
  -    chrome.runtime.onMessage.listen((OnMessageEvent event) {
  +    chrome.runtime.onMessage.listen((event) {
         // TODO(ussuri): Check the sender?
         if (event.message['type'] == 'export_code_response') {
           _codeExported.complete("${event.message['code']}");
  
positive.code:   }
  
    Future _injectScriptIntoWebviewMainWorld(String script) {
      script = script.replaceAll('"', r'\"').replaceAll('\n', r'\n');
      return _executeScriptInWebview(r'''
          (function() {
            var script = document.createElement('script');
            script.innerHTML = '(function() { ''' + script + r'''; })()';
            document.body.appendChild(script);
          })();
      ''');
    }
  
negative.code:     // TODO(ussuri): Check the sender?
      return _injectScriptIntoWebviewMainWorld(r'''
          window.addEventListener("message", function(event) {
            var designer = document.querySelector('#designer');
            var action = event.data['action'];
            if (action === 'export_code') {
              chrome.runtime.sendMessage(
  