Avoid directly using the binary of the
gzipped encoded string in the handler.

Follow up of CL 37431.

Change-Id: Idcd04acb7940e67b7a35b2d6cb163d75b0e22e04
Reviewed-on: https://go-review.googlesource.com/44008
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>