GitLab

- Autogenerate Polymer 3 version of cr-radio-group
- Add to the Polymer 3 demo page
- Add an autogenerated JS module version of event tracker, since this is
used by cr-radio-group
- Autogenerate cr-radio-group v3 automated test.

Bug: 965770
Change-Id: I41034878bb76a769da0c10b37fcf8a698a8f421d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1775582
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Reviewed-by: Esmael Elmoslimany <aee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#692153}