Sync @ fde099a (Oct 26, 2018)

Also update misc/nacl/testzip.proto to include new testdata.
Change-Id: If41590be9f395a591056e89a417b589c4ba71b1a
Reviewed-on: https://go-review.googlesource.com/c/147979
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>