lit/polymer/polyfills uber test script

[aomarks]

It would be handy for being able to quickly test polyfill changes against LitElement and Polymer. We could have a little script in the polyfills monorepo that does this for you.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically closed after being marked stale. If you're still facing this problem with the above solution, please comment and we'll reopen!