Without this, if the responses are compressed, Chrome's content-type
detection will fail and it will attempt to download these pages rather
than render them as HTML.

Change-Id: Ib5f803f335d55a00a759de85d38855ee0ae13ee0
Reviewed-on: https://go-review.googlesource.com/18230Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>