Update golang/go#17606.

Change-Id: I922525561d81a8b7d805729028825953424f6ecc
Reviewed-on: https://go-review.googlesource.com/32912
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>