Add Box object to 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 2deb4bfe77bb8c6865826d5ba712728a7e2abc74..e209eeabb1d2af19a398ea31adc2aa21394369e0 100644
--- a/src/heap-snapshot-generator.h
+++ b/src/heap-snapshot-generator.h
@@ -410,6 +410,7 @@ class V8HeapExplorer : public HeapEntriesAllocator {
   void ExtractAccessorPairReferences(int entry, AccessorPair* accessors);
   void ExtractCodeCacheReferences(int entry, CodeCache* code_cache);
   void ExtractCodeReferences(int entry, Code* code);
+  void ExtractBoxReferences(int entry, Box* box);
   void ExtractCellReferences(int entry, Cell* cell);
   void ExtractPropertyCellReferences(int entry, PropertyCell* cell);
   void ExtractAllocationSiteReferences(int entry, AllocationSite* site);