As noted by Brad in CL 170954 for package bytes.

Change-Id: I2772a356299e54ba5b7884d537e6649039adb9be
Reviewed-on: https://go-review.googlesource.com/c/go/+/171198
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>