net/http: make TimeoutHandler's ResponseWriter implement Pusher
net/http: make TimeoutHandler's ResponseWriter implement Pusher

Fixes #29193

Change-Id: I03088205e51036abbc861ab5b7d141327b0429ae
Reviewed-on: https://go-review.googlesource.com/c/154383
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

josharian/go,cloudflare/go,nawawi/go,nawawi/go,josharian/go,akutz/go,golang/go,golang/go,josharian/go,akutz/go,cloudflare/go,CAFxX/go,golang/go,nawawi/go,cloudflare/go,nawawi/go,akutz/go,cloudflare/go,nawawi/go,akutz/go,josharian/go,cloudflare/go,akutz/go,golang/go,nawawi/go,CAFxX/go,josharian/go,golang/go,CAFxX/go,CAFxX/go,cloudflare/go,CAFxX/go,golang/go,CAFxX/go,golang/go,golang/go,nawawi/go,nawawi/go,cloudflare/go,CAFxX/go,akutz/go,josharian/go,josharian/go,cloudflare/go,akutz/go,akutz/go,josharian/go,CAFxX/go