State of the world:

CL 46430043 introduced a new concurrent sweep but is broken.

CL 62360043 made the new sweep non-concurrent
to try to fix the world while we understand what's wrong with
the concurrent version.

This CL fixes the non-concurrent form to run finalizers.
This CL is just a band-aid to get the build green again.

Dmitriy is working on understanding and then fixing what's
wrong with the concurrent sweep.

TBR=dvyukov
CC=golang-codereviews
https://golang.org/cl/62370043