To rev a179abb (handle Transport PING frames).

Change-Id: I6e1eef2c9586c23f231803d9364d921248722f12
Reviewed-on: https://go-review.googlesource.com/16732Reviewed-by: Blake Mizerany <blake.mizerany@gmail.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>