go.tools/playground/socket: add support for Native Client on arm
go.tools/playground/socket: add support for Native Client on arm

LGTM=minux
R=adg, minux
CC=golang-codereviews
https://codereview.appspot.com/110900043

Committer: Shenghou Ma <72d850dbd8858b791995463d8539b5a379577f28@golang.org>

karmakaze/go.tools,karmakaze/go.tools,karmakaze/go.tools,karmakaze/go.tools,karmakaze/go.tools