http2: add missing test update from CL 200317
http2: add missing test update from CL 200317

I forgot to run the trybots on my CL 200317 and also forgot to include
the test update. Whoops.

Change-Id: I5453f6a7314daa49429b6a3ee49a1b5710c05803
Reviewed-on: https://go-review.googlesource.com/c/net/+/206217
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>

golang/net