Add google-analytics element files.

There are a few additional features I'd like to add, but I wanted to get the base stuff committed first.

In the future I think we can remove the dependency on the [Embed API](https://developers.google.com/analytics/devguides/reporting/embed/v1/) completely and just use `<google-chart>` and something like `<core-ajax>`, but for now this is working pretty well.
I could, but then it'd need to be in the global scope. I think such a change would require a bit of planning to discuss what global namespace to use. Perhaps we can hold off on this until a later date?