There's no shim.

For the fullscreen bubble we made ExclusiveAccessControllerViews to bridge the gap - https://cs.chromium.org/chromium/src/chrome/browser/ui/cocoa/browser/exclusive_access_controller_views.h?ssfr=1

It nicely fits the "favour composition over inheritance" guideline that we suggest at https://chromium.googlesource.com/chromium/src/+/master/styleguide/c++/c++.md#Multiple-inheritance

(i.e. https://codereview.chromium.org/1650483002 moved ExclusiveAccessContext from a parent of BrowserWindowCocoa to a component).

We probably need something similar for FindBarHost

Anyway I think we are already tracking this in  Issue 673589  - there are some notes there