chown is not implemented on js: see https://build.golang.org/log/43d7b12602660b786a6e080e685165193df0de00.

Change-Id: I3f461338825bb670d682c3f47b17ee1638343fc8
Reviewed-on: https://go-review.googlesource.com/c/154097
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>