Fix timer flaky test in lollipop-mr1-cts-dev.

It is partically cherry-pick from https://android-review.googlesource.com/#/c/123410/.
And as lollipop-mr1-cts-dev still uses stlport, <stdatomic.h> is used instead of <atomic>.

Bug: 20677618
Change-Id: I952a6fd074facc4227c955fecf3ecbfbbaec4193
1 file changed