Support ES6 weak collections in heap profiler

src/heap-snapshot-generator.h

Index: src/heap-snapshot-generator.h
diff --git a/src/heap-snapshot-generator.h b/src/heap-snapshot-generator.h
index e1c291e90147f6b99dfc9bab2817e8a7c70ef4de..b45607fceb247e05781bdef677e3e41b33f80470 100644
--- a/src/heap-snapshot-generator.h
+++ b/src/heap-snapshot-generator.h
@@ -370,6 +370,8 @@ class V8HeapExplorer : public HeapEntriesAllocator {
   void ExtractJSObjectReferences(int entry, JSObject* js_obj);
   void ExtractStringReferences(int entry, String* obj);
   void ExtractSymbolReferences(int entry, Symbol* symbol);
+  void ExtractJSWeakCollectionReferences(int entry,
+                                         JSWeakCollection* collection);
   void ExtractContextReferences(int entry, Context* context);
   void ExtractMapReferences(int entry, Map* map);
   void ExtractSharedFunctionInfoReferences(int entry,