On SitePoint's PHP blog Taylor Ren has posted the second part of his series looking at integrating Polymer/Dart and the Symfony framework to make a simple browser-based widget. The first part of the series can be found here.
If the server (and thus the configuration, the programming) is managed by ourselves, the process to get data from a RESTful API from that same server will be simple. We can enable CORS in the returned response header. Done! But if the remote server's RESTful API does not set that header, we will face a CORS error when we try to invoke that API call from within the Dart app.
He offers one solution - JSONP - but dismisses it because of its "hacky nature". Instead he opts to use the PHP (Symfony) side to grab the data from the remote feeds and pull it into the local domain for the widget to fetch. Code for both the client side and server side functionality are included as well as the HTML markup to create the page for the widget.