name           old time/op    new time/op    delta
ServerPosts-4     192µs ± 1%     164µs ± 1%  -14.16%  (p=0.000 n=17+19)

name           old alloc/op   new alloc/op   delta
ServerPosts-4    69.8kB ± 0%     2.8kB ± 0%  -95.95%  (p=0.000 n=18+18)

name           old allocs/op  new allocs/op  delta
ServerPosts-4      42.0 ± 0%      40.0 ± 0%   -4.76%  (p=0.000 n=20+20)

This is a redo of git rev e7da8eda (golang.org/cl/20542) which had a race
and was later reverted in golang.org/cl/21160.

Updates golang/go#14960
Updates grpc/grpc-go#604

Change-Id: Ie216e45730dce4fc0c58f295bcbc669973145599
Reviewed-on: https://go-review.googlesource.com/31447
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>