Replace bool by atomic_bool in multithreaded test (#3009)
Replace bool by atomic_bool in multithreaded test (#3009)

TSAN was complaining about the usage of a non-synchronized variable. I
could have either introduced another mutex or made the variable atomic.
I chose the latter, mainly because there is already a mutex with a
different purpose and I didn't wanna make it easier to confuse the two
mutexes.
google/orbit,google/orbit,google/orbit,google/orbit