testing: fix divide by zero when benchmark is faster than OS's clock resolution
I did not added a test because `benchmark_test.go` is `package testing_test`
and I don't care to change that because calling predictN is not testing the
thing I would want to test.
Ideally we would run benchmark in a VM with a highjacked clocksource that never
marches forward, or using faketime but that looks fairly involved for a quickie
fix.
Fixes #70709
Change-Id: I8b4d697aff7cba33da388cb0ae8e2c2b550b9690
Reviewed-on: https://go-review.googlesource.com/c/go/+/633419 Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Jorropo <jorropo.pgm@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Keith Randall <khr@golang.org> Reviewed-by: Keith Randall <khr@google.com>