Handle cross-thread weak persistents during global weak processing.

third_party/WebKit/Source/platform/heap/MarkingVisitorImpl.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MarkingVisitorImpl_h
 #define MarkingVisitorImpl_h
 
 #include "platform/heap/Heap.h"
 #include "platform/heap/ThreadState.h"
 #include "platform/heap/Visitor.h"
@@ skipping 86 matching lines @@
         // Inline what the above markNoTracing() call expands to,
         // so as to make sure that we do get all the benefits.
         HeapObjectHeader* header = HeapObjectHeader::fromPayload(objectPointer);
         if (header->isMarked())
             return false;
         header->mark();
 #endif
         return true;
     }
 
-    Derived* toDerived()
-    {
-        return static_cast<Derived*>(this);
-    }
-
-protected:
     inline void registerWeakCellWithCallback(void** cell, WeakCallback callback)
     {
         ASSERT(toDerived()->getMarkingMode() != Visitor::WeakProcessing);
         // We don't want to run weak processings when taking a snapshot.
         if (toDerived()->getMarkingMode() == Visitor::SnapshotMarking)
             return;
         toDerived()->heap().pushGlobalWeakCallback(cell, callback);
     }
 
+    Derived* toDerived()
+    {
+        return static_cast<Derived*>(this);
+    }
+
 private:
     static void markNoTracingCallback(Visitor* visitor, void* object)
     {
         visitor->markNoTracing(object);
     }
 };
 
 } // namespace blink
 
 #endif