[heap profiler] Use std::atomic

Change-Id: I43128135bdb488ad92c749b6ff33811fb429f6fc
Reviewed-on: https://chromium-review.googlesource.com/c/1454088
Commit-Queue: Alexei Filippov <alph@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629321}
2 files changed