use atomic for global test counters

TSAN is failing because
multiple threads are incrementing the
same global

TBR=mtklein@google.com

Bug: skia:
Change-Id: I9c3bc6bb4aa7cbe7ced5b3080790d3c4ad1ff798
Reviewed-on: https://skia-review.googlesource.com/146446
Commit-Queue: Cary Clark <caryclark@skia.org>
Reviewed-by: Cary Clark <caryclark@skia.org>
Auto-Submit: Cary Clark <caryclark@skia.org>
6 files changed