Once the native media controls ship 100%, we should remove MR extensions from the extensionview whitelist.

https://cs.chromium.org/chromium/src/extensions/browser/guest_view/extension_view/whitelist/extension_view_whitelist.cc?rcl=7242c905623f9f5243e757e3fbaa35298e9c8c30&l=22

As MR is the only extension in this whitelist we may be able to then remove extensionview support entirely (need to check w/extensions team)