It's apparent from the file names or build tags to which OS the code in
question applies.

Change-Id: I628ee2bf1d29a6bc30ca5fa6f9eecf809e78a182
Reviewed-on: https://go-review.googlesource.com/110815
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>