http2: add DialTLS to Transport

This commit allows a client of Transport to supply their own Dial
function that assumes all TLS checks have been performed and the
returned net.Conn is an h2 ready client connection.

Change-Id: If35b5c47c3bd6912a990d6cd89feefa3303bb42b
Reviewed-on: https://go-review.googlesource.com/16289
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
2 files changed