Still have to rely on webextension-polyfill, but, hopefully, it's not long until #Chrome will expose Extension APIs under browser.* namespace, just like #Firefox.
https://issues.chromium.org/issues/40556351
Meanwhile, TIL how to build a cross-browser extension: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Build_a_cross_browser_extension