testing: read coverage counters atomically For -mode=atomic, we need to read the counters using an atomic load to avoid a race. Not worth worrying about when -mode=atomic is set during generation of the profile, so we use atomic loads always.
testing: read coverage counters atomically
For -mode=atomic, we need to read the counters
using an atomic load to avoid a race. Not worth worrying
about when -mode=atomic is set during generation
of the profile, so we use atomic loads always.

Fixes issue 8630.

LGTM=rsc
R=dvyukov, rsc
CC=golang-codereviews
https://codereview.appspot.com/141800043

firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang,wesolows/golang,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old