Wow, I have no idea how this one flaked, it looks really simple.

https://cs.chromium.org/chromium/src/base/synchronization/read_write_lock_unittest.cc?l=184

Oh, it's not just a plain base::Lock mutex, it's going through different pthreads functions https://cs.chromium.org/chromium/src/base/synchronization/read_write_lock_posix.cc?l=29 rather than a plain-ish (?) https://cs.chromium.org/chromium/src/base/synchronization/lock_impl_posix.cc?&l=62 .

Could it be a legit Fuchsia bug instead of a base_unittests bug this time??! Tune in after the break for all the juicy details.