anchor.diff:        return new Timer(new Duration(milliseconds: 500), () {
           // The request is received and handled by the JS proxy script injected
           // into [_webview>] by [_injectDesignerProxy].
  -        return _executeScriptInWebview('''
  -            window.postMessage({action: 'import_code', code: '$code'}, '*');
  +        return _executeScriptInWebview(r'''
  +            window.postMessage(
  +                {action: 'import_code', code: ''' + code + r'''}, '*');
           ''');
         });
       });
  
positive.code: import 'dart:async';
  import 'dart:html';
  import 'dart:js' as js;
  
  import 'package:chrome/chrome_app.dart' as chrome;
  import 'package:polymer/polymer.dart';
  
negative.code:       // asynchronously returns the result via a chrome.runtime.sendMessage,
        // received and handled by [_designProxyListener], which completes the
        // [_codeExported] completer with the code string.
        _executeScriptInWebview(r'''
            window.postMessage({action: 'export_code'}, '*');
        ''');
      });
  