Cheaper thread-safe atomic initialization of static references.

Source/core/workers/WorkerThread.cpp

Index: Source/core/workers/WorkerThread.cpp
diff --git a/Source/core/workers/WorkerThread.cpp b/Source/core/workers/WorkerThread.cpp
index a08d7c5ec5afcd791cf69cdad1a0558aedfa4ffb..6a3f9e5bcccdfbce3424f4cc6c33cc3b74de16d4 100644
--- a/Source/core/workers/WorkerThread.cpp
+++ b/Source/core/workers/WorkerThread.cpp
@@ -71,7 +71,7 @@ public:
 
 static Mutex& threadSetMutex()
 {
-    AtomicallyInitializedStatic(Mutex&, mutex = *new Mutex);
+    AtomicallyInitializedStaticReference(Mutex, mutex, new Mutex);
     return mutex;
 }