[Feature Request] client:plusone library

[Scarygami]

One common scenario when using the Google JS Client library is to load client.js and plusone.js at the same time with this URL: https://apis.google.com/js/client:plusone.js

I would suggest to have a matching <google-client-plusone-api> element.

I'm aware that you could use <google-client-api> + <google-plusone-api> but then you would have to wait for two separate api-load events to finish, which adds unnecessary complexity.