bc37920bdb
There are no callers from JS (looked at the selection region constant usage in idl and those use nsISelectionController, not this). If we were to provide this API in the future, it would probably use ScrollIntoViewOptions or so instead (plus something extra perhaps). I wanted to remove the weird WehreToScroll percentage impl, but actually some C++ accessibility code still uses it. Differential Revision: https://phabricator.services.mozilla.com/D216872