CL 150417 was submitted before I could recommend this change to remove
an unnecessary allocation.

Updates #28849

Change-Id: I4cd655f62bb3d00eda6c997f074785385bceee0c
Reviewed-on: https://go-review.googlesource.com/c/150498Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>