CrossThreadPersistentRegion will only trace objects belonging to the current GCing ThreadHeap

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

 // Copyright 2015 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 PersistentNode_h
 #define PersistentNode_h
 
 #include "platform/PlatformExport.h"
 #include "platform/heap/ThreadState.h"
 #include "wtf/Allocator.h"
@@ skipping 132 matching lines @@
     void freePersistentNode(PersistentNode* persistentNode)
     {
         ASSERT(m_persistentCount > 0);
         persistentNode->setFreeListNext(m_freeListHead);
         m_freeListHead = persistentNode;
 #if ENABLE(ASSERT)
         --m_persistentCount;
 #endif
     }
 
+    static bool shouldTracePersistentNode(Visitor*, PersistentNode*) { return true; }
+
     void releasePersistentNode(PersistentNode*, ThreadState::PersistentClearCallback);
-    void tracePersistentNodes(Visitor*);
+    using ShouldTraceCallback = bool (*)(Visitor*, PersistentNode*);
+    void tracePersistentNodes(Visitor*, ShouldTraceCallback = PersistentRegion::shouldTracePersistentNode);
     int numberOfPersistents();
 
 private:
     friend CrossThreadPersistentRegion;
 
     void ensurePersistentNodeSlots(void*, TraceCallback);
 
     PersistentNode* m_freeListHead;
     PersistentNodeSlots* m_slots;
 #if ENABLE(ASSERT)
@@ skipping 14 matching lines @@
 
     void freePersistentNode(PersistentNode* persistentNode)
     {
         MutexLocker lock(m_mutex);
         m_persistentRegion->freePersistentNode(persistentNode);
     }
 
     void tracePersistentNodes(Visitor* visitor)
     {
         MutexLocker lock(m_mutex);
-        m_persistentRegion->tracePersistentNodes(visitor);
+        m_persistentRegion->tracePersistentNodes(visitor, CrossThreadPersistentRegion::shouldTracePersistentNode);
     }
 
     void prepareForThreadStateTermination(ThreadState*);
 
+    static bool shouldTracePersistentNode(Visitor*, PersistentNode*);
+
 private:
     // We don't make CrossThreadPersistentRegion inherit from PersistentRegion
     // because we don't want to virtualize performance-sensitive methods
     // such as PersistentRegion::allocate/freePersistentNode.
     OwnPtr<PersistentRegion> m_persistentRegion;
     Mutex m_mutex;
 };
 
 } // namespace blink
 
 #endif