Fix perf regression in blink_perf.shadow_dom.

Source/platform/heap/Visitor.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 23 matching lines @@
 #include "platform/PlatformExport.h"
 #include "platform/heap/GarbageCollected.h"
 #include "platform/heap/StackFrameDepth.h"
 #include "platform/heap/ThreadState.h"
 #include "wtf/Assertions.h"
 #include "wtf/Atomics.h"
 #include "wtf/Deque.h"
 #include "wtf/Forward.h"
 #include "wtf/HashMap.h"
 #include "wtf/HashTraits.h"
+#include "wtf/InstanceCounter.h"
+#include "wtf/Threading.h"
 #include "wtf/TypeTraits.h"
-#if ENABLE(GC_PROFILING)
-#include "wtf/InstanceCounter.h"
 #include "wtf/text/WTFString.h"
-#endif
 
 namespace blink {
 
 template<typename T> class GarbageCollected;
 class HeapObjectHeader;
 class InlinedGlobalMarkingVisitor;
 template<typename T> class TraceTrait;
 template<typename T> class TraceEagerlyTrait;
 class Visitor;
 
@@ skipping 325 matching lines @@
 
     const MarkingMode m_markingMode;
     bool m_isGlobalMarkingVisitor;
 };
 
 template<typename T>
 struct TypenameStringTrait {
     // This method is not thread safe.
     static const String& get()
     {
-        DEFINE_STATIC_LOCAL(String, typenameString, (WTF::extractTypeNameFromFunctionName(WTF::extractNameFunction<T>())));
+        AtomicallyInitializedStaticReference(AtomicString, typenameString, new AtomicString(WTF::extractTypeNameFromFunctionName(WTF::extractNameFunction<T>())));
         return typenameString;
     }
 };
 
 } // namespace blink
 
 #endif // Visitor_h