I'd like to introduce kSynthetic type of nodes for Heap Profiler.

src/profile-generator.h

 // Copyright 2011 the V8 project authors. 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
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 507 matching lines @@
  public:
   enum Type {
     kHidden = v8::HeapGraphNode::kHidden,
     kArray = v8::HeapGraphNode::kArray,
     kString = v8::HeapGraphNode::kString,
     kObject = v8::HeapGraphNode::kObject,
     kCode = v8::HeapGraphNode::kCode,
     kClosure = v8::HeapGraphNode::kClosure,
     kRegExp = v8::HeapGraphNode::kRegExp,
     kHeapNumber = v8::HeapGraphNode::kHeapNumber,
-    kNative = v8::HeapGraphNode::kNative
+    kNative = v8::HeapGraphNode::kNative,
+    kSynthetic = v8::HeapGraphNode::kSynthetic
   };
 
   HeapEntry() { }
   void Init(HeapSnapshot* snapshot,
             Type type,
             const char* name,
             uint64_t id,
             int self_size,
             int children_count,
             int retainers_count);
@@ skipping 480 matching lines @@
   static HeapObject* const kFirstGcSubrootObject;
   static HeapObject* const kLastGcSubrootObject;
 
   friend class IndexedReferencesExtractor;
   friend class GcSubrootsEnumerator;
   friend class RootsReferencesExtractor;
 
   DISALLOW_COPY_AND_ASSIGN(V8HeapExplorer);
 };
 
+
 class NativeGroupRetainedObjectInfo;
 
+
 // An implementation of retained native objects extractor.
-class NativeObjectsExplorer : public HeapEntriesAllocator {
+class NativeObjectsExplorer {
  public:
   NativeObjectsExplorer(HeapSnapshot* snapshot,
                       SnapshottingProgressReportingInterface* progress);
   virtual ~NativeObjectsExplorer();
-  virtual HeapEntry* AllocateEntry(
-      HeapThing ptr, int children_count, int retainers_count);
   void AddRootEntries(SnapshotFillerInterface* filler);
   int EstimateObjectsCount();
   bool IterateAndExtractReferences(SnapshotFillerInterface* filler);
 
  private:
   void FillRetainedObjects();
   void FillImplicitReferences();
   List<HeapObject*>* GetListMaybeDisposeInfo(v8::RetainedObjectInfo* info);
   void SetNativeRootReference(v8::RetainedObjectInfo* info);
   void SetRootNativeRootsReference();
@@ skipping 18 matching lines @@
   NativeGroupRetainedObjectInfo* FindOrAddGroupInfo(const char* label);
 
   HeapSnapshot* snapshot_;
   HeapSnapshotsCollection* collection_;
   SnapshottingProgressReportingInterface* progress_;
   bool embedder_queried_;
   HeapObjectsSet in_groups_;
   // RetainedObjectInfo* -> List<HeapObject*>*
   HashMap objects_by_info_;
   HashMap native_groups_;
+  HeapEntriesAllocator* synthetic_entries_allocator_;
+  HeapEntriesAllocator* native_entries_allocator_;
   // Used during references extraction.
   SnapshotFillerInterface* filler_;
 
   static HeapThing const kNativesRootObject;
 
   friend class GlobalHandlesExtractor;
 
   DISALLOW_COPY_AND_ASSIGN(NativeObjectsExplorer);
 };
 
@@ skipping 78 matching lines @@
 
   friend class HeapSnapshotJSONSerializerEnumerator;
   friend class HeapSnapshotJSONSerializerIterator;
 
   DISALLOW_COPY_AND_ASSIGN(HeapSnapshotJSONSerializer);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_PROFILE_GENERATOR_H_