The snackbar is placed depending on the toolbar so the relation should be
reversed. The toolbar should not know about and control the snackbar.
There could be other siblings that the snackbar wants to position itself by
and so removing this responsability from BrowserToolbarBehavior will help
better support current and future flows.

Backport of https://github.com/mozilla-mobile/firefox-android/commit/04a464e66a95892d9ac7929974da51116cd1585d

This will allow clients easily implement their own UI.

Backport of https://github.com/mozilla-mobile/firefox-android/commit/e678610bc10df96b8543c26fb5eb7c1ba26e3e20

This will allow clients easily implement their own UI

Backport of https://github.com/mozilla-mobile/firefox-android/commit/c53dd65718579006e174803acf683ffd44075049

Backport of https://github.com/mozilla-mobile/firefox-android/commit/1dc21a3786506200be124733e654dff8f39b5395