Updating to commit dec22b42d9eee442222c36c8da24ddc9905e7ee6
from github.com/google/pprof

Fixes #19322.

Change-Id: I1bc3fcd381f22d52557f61c6fb694f54fc64470c
Reviewed-on: https://go-review.googlesource.com/37652Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>