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

src/profile-generator.cc

Index: src/profile-generator.cc
diff --git a/src/profile-generator.cc b/src/profile-generator.cc
index 61d7e80cde5af585aa33872854a53209455cbad1..02b9408cff3d326e4ce9f377d59b088cf246a804 100644
--- a/src/profile-generator.cc
+++ b/src/profile-generator.cc
@@ -1131,6 +1131,7 @@ const char* HeapEntry::TypeAsString() {
     case kRegExp: return "/regexp/";
     case kHeapNumber: return "/number/";
     case kNative: return "/native/";
+    case kArtificial: return "/artificial/";
     default: return "???";
   }
 }
@@ -2738,7 +2739,7 @@ HeapEntry* NativeObjectsExplorer::AllocateEntry(
   intptr_t elements = info->GetElementCount();
   intptr_t size = info->GetSizeInBytes();
   return snapshot_->AddEntry(
-      HeapEntry::kNative,
+      static_cast<HeapEntry::Type>(info->GetType()),
       elements != -1 ?
           collection_->names()->GetFormatted(
               "%s / %" V8_PTR_PREFIX "d entries",
@@ -2862,6 +2863,9 @@ class NativeGroupRetainedObjectInfo : public v8::RetainedObjectInfo {
   }
   virtual intptr_t GetHash() { return hash_; }
   virtual const char* GetLabel() { return label_; }
+  virtual HeapGraphNode::Type GetType() const {
+    return HeapGraphNode::kArtificial;
+  }
 
  private:
   bool disposed_;
@@ -3547,7 +3551,8 @@ void HeapSnapshotJSONSerializer::SerializeNodes() {
             "," JSON_S("closure")
             "," JSON_S("regexp")
             "," JSON_S("number")
-            "," JSON_S("native"))
+            "," JSON_S("native")
+            "," JSON_S("artificial"))
         "," JSON_S("string")
         "," JSON_S("number")
         "," JSON_S("number")