Updating to commit 79c4198ef7bd1069f8f56501fc05f0f1d2c33d8a
from github.com/google/pprof

Fixes #22561.

Change-Id: Ib92fd443ccc067aef7214e59f594db7f2521535b
Reviewed-on: https://go-review.googlesource.com/75870
Run-TryBot: David du Colombier <0intro@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>