Fix race at blink::GCInfoAtBase<T>::index

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/MainThread.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;
@@ skipping 329 matching lines @@
     static Visitor* fromHelper(VisitorHelper<Visitor>* helper) { return static_cast<Visitor*>(helper); }
 
     const MarkingMode m_markingMode;
     bool m_isGlobalMarkingVisitor;
 };
 
 template<typename T>
 struct TypenameStringTrait {
     static const String& get()
     {
+        ASSERT(isMainThread());

[haraken, 2015/08/12 12:33:41]

It is not guaranteed that get() is called only by the main thread. It is called
by any GCing thread, which is not necessarily the main thread.

Can we use AtomicallyInitializedStaticReference so that non-main threads can
call get() safely?

         DEFINE_STATIC_LOCAL(String, typenameString, (WTF::extractTypeNameFromFunctionName(WTF::extractNameFunction<T>())));
         return typenameString;
     }
 };
 
 } // namespace blink
 
 #endif // Visitor_h