We import the ActorConstants into the ASRouter unit-entry.js script because ASRouterChild.sys.mjs loads ActorConstants.sys.mjs, and the ResourceUriPlugin that does the rewriting for the Karma tests doesn't understand how to do remapping outside of the newtab folder. So instead of trying to hack that capability into ResourceUriPlugin, we just import the ActorConstants into the Karma global scope. Differential Revision: https://phabricator.services.mozilla.com/D200087