Extended Description

Chrome and all of its test binaries fail when built in a debug build on arm32. We bisected this down to r304267.

https://bugs.chromium.org/p/chromium/issues/detail?id=742563#c15 has some analysis on what's wrong. The file mentioned there is https://cs.chromium.org/chromium/src/base/threading/thread_local_storage.cc?q=base/threading/thread_local_storage.cc&sq=package:chromium&dr&l=320

TlsVectorEntry* tls_data = static_cast<TlsVectorEntry*>(
PlatformThreadLocalStorage::GetTLSValue(
base::subtle::NoBarrier_Load(&g_native_tls_key)));
if (!tls_data)
tls_data = ConstructTlsVector();
DCHECK_NE(slot_, kInvalidSlotValue);
DCHECK_LT(slot_, kThreadLocalStorageSize);
tls_data[slot_].data = value;
tls_data[slot_].version = version_;

"First ThreadLocalStorage::StaticSlot::Set(void* value) gets called, then when ThreadLocalStorage::StaticSlot::Get() is called later on, tls_data is null, and ConstructTlsVector() is called again." (this is the bug)