To pull in the fix for #28858, which we want to include for Go 1.12.

Fixes #28858.

Change-Id: Id4964cfd38e3d44d6317a2ee124fe2d35038b5fd
Reviewed-on: https://go-review.googlesource.com/c/152277
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>