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.
Note, requiring this branch is needed until [this pull request](https://github.com/GoogleWebComponents/google-chart/pull/4) is merged. I can update afterward...