Full error:

1589:775:1218/223456.229690:FATAL:thread_restrictions.cc(116)] Check failed: !g_base_sync_primitives_disallowed.Get().Get(). Waiting on a //base sync primitive is not allowed on this thread to prevent jank and deadlock. If waiting on a //base sync primitive is unavoidable, do it within the scope of a ScopedAllowBaseSyncPrimitives. If in a test, use ScopedAllowBaseSyncPrimitivesForTesting.
0   Chromium Framework                  0x000000011917a75f base::debug::StackTrace::StackTrace(unsigned long) + 31
1   Chromium Framework                  0x0000000119076f3f logging::LogMessage::~LogMessage() + 223
2   Chromium Framework                  0x00000001191411f9 base::internal::AssertBaseSyncPrimitivesAllowed() + 121
3   Chromium Framework                  0x00000001191396ed base::internal::ScopedBlockingCallWithBaseSyncPrimitives::ScopedBlockingCallWithBaseSyncPrimitives(base::BlockingType) + 141
4   Chromium Framework                  0x0000000119188790 base::PlatformThread::Join(base::PlatformThreadHandle) + 48
5   Chromium Framework                  0x000000011913d629 base::Thread::Stop() + 137
6   Chromium Framework                  0x00000001190c9ef9 base::StackSamplingProfiler::SamplingThread::GetOrCreateTaskRunnerForAdd() + 297
7   Chromium Framework                  0x00000001190c9cbe base::StackSamplingProfiler::SamplingThread::Add(std::__1::unique_ptr<base::StackSamplingProfiler::SamplingThread::CollectionContext, std::__1::default_delete<base::StackSamplingProfiler::SamplingThread::CollectionContext> >) + 46
8   Chromium Framework                  0x00000001190cb932 base::StackSamplingProfiler::Start() + 626
9   Chromium Framework                  0x00000001191c4b8a ThreadProfiler::StartPeriodicSamplingCollection() + 426
10  Chromium Framework                  0x00000001191c5397 base::internal::Invoker<base::internal::BindState<void (ThreadProfiler::*)(), base::WeakPtr<ThreadProfiler> >, void ()>::RunOnce(base::internal::BindStateBase*) + 183

Suspecting https://crrev.com/c/1283010 "[PlatformThread] Join() is a wait, update assertions as such." by Gabriel Charette. 

Failing builds:

https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20FYI%20Experimental%20Release%20%28Intel%29/7486
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20FYI%20Release%20%28Intel%29/9276
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20FYI%2010.14%20Release%20%28Intel%29/731
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20Pro%20FYI%20Release%20%28AMD%29/3601
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20FYI%20Experimental%20Retina%20Release%20%28AMD%29/8047
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20FYI%2010.14%20Release%20%28AMD%29/645

Several more too. We should probably temporarily revert this to unblock the mac_optional_gpu_tests_rel bot and the ANGLE CQ. Unsure what labels to use here.