CrossThreadPersistentRegion will only trace objects belonging to the current GCing ThreadHeap

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

Index: third_party/WebKit/Source/platform/heap/PersistentNode.h
diff --git a/third_party/WebKit/Source/platform/heap/PersistentNode.h b/third_party/WebKit/Source/platform/heap/PersistentNode.h
index 7b94bbe75cd648efd4afae60c592ced48c85b665..52b558084cb0772fac38b2915c8fc591c9e614d5 100644
--- a/third_party/WebKit/Source/platform/heap/PersistentNode.h
+++ b/third_party/WebKit/Source/platform/heap/PersistentNode.h
@@ -150,8 +150,11 @@ public:
 #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:
@@ -186,11 +189,13 @@ public:
     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