Copied by hand.

Update #17410
Update #19142
Fixes #19986

Change-Id: I21d16d254161c75466b31c670f3b2c8c463abd66
Reviewed-on: https://go-review.googlesource.com/41205
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>