Handle cross-thread weak persistents during global weak processing.

third_party/WebKit/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 300 matching lines @@
     virtual void registerWeakMembers(const void*, const void*, WeakCallback) = 0;
     using VisitorHelper<Visitor>::registerWeakMembers;
 
     virtual void registerWeakTable(const void*, EphemeronCallback, EphemeronCallback) = 0;
 #if ENABLE(ASSERT)
     virtual bool weakTableRegistered(const void*) = 0;
 #endif
 
     virtual bool ensureMarked(const void*) = 0;
 
+    virtual void registerWeakCellWithCallback(void**, WeakCallback) = 0;
+
     inline MarkingMode getMarkingMode() const { return m_markingMode; }
 
 protected:
     Visitor(ThreadState*, MarkingMode);
 
-    virtual void registerWeakCellWithCallback(void**, WeakCallback) = 0;
-
 private:
     static Visitor* fromHelper(VisitorHelper<Visitor>* helper) { return static_cast<Visitor*>(helper); }
 
     ThreadState* m_state;
     const MarkingMode m_markingMode;
 };
 
 } // namespace blink
 
 #endif // Visitor_h