Also, the use of AtomicRefCount to check for cross-thread use of non-atomic
RefCounted is suspect (the guarantees provided by AtomicRefCount aren't
obviously strong enough for this use). Since this is only used for DCHECKs,
it seems simplest to have it use sequentially-consistent atomics and not
think about it further.

Bug: 736037
Tbr: sky@chromium.org
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I1613e5f39fa814ceef3cec5bd25806179b65c978
Reviewed-on: https://chromium-review.googlesource.com/556014


Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Taiju Tsuiki <tzik@chromium.org>
Cr-Commit-Position: refs/heads/master@{#484700}