Add a thread-safety assertion in DEFINE_STATIC_LOCAL

Source/wtf/ThreadingPthreads.cpp

Index: Source/wtf/ThreadingPthreads.cpp
diff --git a/Source/wtf/ThreadingPthreads.cpp b/Source/wtf/ThreadingPthreads.cpp
index 2208ca4e9a863411ba69a3ee9b52c6c221a96ceb..91e7ef7889c6be5f20872e0de420234a3927543d 100644
--- a/Source/wtf/ThreadingPthreads.cpp
+++ b/Source/wtf/ThreadingPthreads.cpp
@@ -246,6 +246,33 @@ void ThreadCondition::broadcast()
     ASSERT_UNUSED(result, !result);
 }
 
+#if ENABLE(ASSERT)
+static bool s_threadCreated = false;
+
+struct ThreadCreationRecorder {
+    ThreadCreationRecorder()
+    {
+        ASSERT(!s_threadCreated);
+        s_threadCreated = true;
+    }
+};
+
+bool isAtomicallyInitializedStaticMutexLockHeld()
+{
+    return atomicallyInitializedStaticMutex && atomicallyInitializedStaticMutex->locked();
+}
+
+bool isBeforeThreadCreated()
+{
+    return !s_threadCreated;
+}
+
+void willCreateThread()
+{
+    static ThreadCreationRecorder recorder;
+}
+#endif
+
 } // namespace WTF
 
 #endif // USE(PTHREADS)