Use TLS storage for thread ids in wtf/ThreadingPThreads

third_party/WebKit/Source/wtf/ThreadSpecific.h

Index: third_party/WebKit/Source/wtf/ThreadSpecific.h
diff --git a/third_party/WebKit/Source/wtf/ThreadSpecific.h b/third_party/WebKit/Source/wtf/ThreadSpecific.h
index 5d7f6d26a9eba250c76907a791b1e34b80de2c5d..377a82f4e24e405aafb5c707a672de58ddc39ce6 100644
--- a/third_party/WebKit/Source/wtf/ThreadSpecific.h
+++ b/third_party/WebKit/Source/wtf/ThreadSpecific.h
@@ -224,11 +224,6 @@ inline void ThreadSpecific<T>::set(T* ptr) {
 
 template <typename T>
 inline void ThreadSpecific<T>::destroy(void* ptr) {
-  // Never call destructors on the main thread.
-  // This is fine because Blink no longer has a graceful shutdown sequence.
-  if (isMainThread())
-    return;
-
   Data* data = static_cast<Data*>(ptr);
 
 #if OS(POSIX)
@@ -238,6 +233,13 @@ inline void ThreadSpecific<T>::destroy(void* ptr) {
   pthread_setspecific(data->owner->m_key, ptr);
 #endif
 
+  // Never call destructors on the main thread. This is fine because Blink no
+  // longer has a graceful shutdown sequence. Be careful to call this function
+  // (which can be re-entrant) while the pointer is still set, to avoid lazily
+  // allocating WTFThreadData after it is destroyed.
+  if (isMainThread())
+    return;
+
   data->value->~T();
   Partitions::fastFree(data->value);