This reverts CL 111676 for golang/go#25023.

Reason for revert: The code change no longer issued a WindowUpdate which
is required when processing data. The original issue found in golang/go#25023
is not present after the revert.

Updates golang/go#28204

Change-Id: Iadbb63d50ca06df1281e699b9ef13181d0593f80
Reviewed-on: https://go-review.googlesource.com/c/153977Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>