Use std::atomic_ulong for CreateUniqueIdentifier()

We will use CreateUniqueIdentifier() from worker threads when off-main-thread-fetch is enabled.
So g_unique_identifier must be atomic.

Bug: 443374
Change-Id: I766f466c250a90a8e2e61c8ac5535d3144a909b6
Reviewed-on: https://chromium-review.googlesource.com/593467
Commit-Queue: Tsuyoshi Horo <horo@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#490829}
1 file changed