Use __tsan_atomic64 instead of long in Atomics.h
Use __tsan_atomic64 instead of long in Atomics.h

For readability, we should use __tsan_atomic64 instead of long.

Also TSan doesn't (or is not planning to) support 32 bit.
So this CL removes 32 bit code from TSan functions.

BUG=474320

Review URL: https://codereview.chromium.org/1066253004

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@193412 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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