Updates #29919

Change-Id: Ibf92c9957f71394f08c1203a29eae35a12021585
Reviewed-on: https://go-review.googlesource.com/c/159877
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>