It seems this branch is not needed anymore. It was originally added in
1999 to support gtk_widget_realize(), but all those reasons seem
obsolete today.
Instead just call gtk_widget_realize().

If you end up at this commit when bisecting:
There is no bug that made me remove this code, it was purely meant to be
cleanup / dead code removal. I seem to have introduced a new bug or
bisecting wouldn't have let you here. So it seems we should just revert
this commit.