This causes a performance regression for some calls.

Fixes #23424.
Updates #6853.

Change-Id: Id1db652d5aca0ce631a3417c0c056d6637fefa9e
Reviewed-on: https://go-review.googlesource.com/88135
Run-TryBot: Caleb Spare <cespare@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>