Make |Heap::findGCInfo()| threadsafe.

Source/platform/heap/ThreadState.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 477 matching lines @@
 
     // Visit all persistents allocated on this thread.
     void visitPersistents(Visitor*);
 
     // Checks a given address and if a pointer into the oilpan heap marks
     // the object to which it points.
     bool checkAndMarkPointer(Visitor*, Address);
 
 #if ENABLE(GC_TRACING)
     const GCInfo* findGCInfo(Address);
+    static const GCInfo* findGCInfoFromAllThreads(Address);
 #endif
 
     void pushWeakObjectPointerCallback(void*, WeakPointerCallback);
     bool popAndInvokeWeakPointerCallback(Visitor*);
 
     void getStats(HeapStats&);
     HeapStats& stats() { return m_stats; }
     HeapStats& statsAfterLastGC() { return m_statsAfterLastGC; }
 
 private:
@@ skipping 88 matching lines @@
 };
 
 template<> class ThreadStateFor<AnyThread> {
 public:
     static ThreadState* state() { return ThreadState::current(); }
 };
 
 }
 
 #endif // ThreadState_h