Add WeakCell support to heap profiler.

src/profiler/heap-snapshot-generator.h

Index: src/profiler/heap-snapshot-generator.h
diff --git a/src/profiler/heap-snapshot-generator.h b/src/profiler/heap-snapshot-generator.h
index 949df26cdef2fd0818573f355ff9e3f11c56e890..5267fce00d51e81dbff4a3d7a4947bc3b420dd22 100644
--- a/src/profiler/heap-snapshot-generator.h
+++ b/src/profiler/heap-snapshot-generator.h
@@ -385,6 +385,7 @@ class V8HeapExplorer : public HeapEntriesAllocator {
   void ExtractCodeReferences(int entry, Code* code);
   void ExtractBoxReferences(int entry, Box* box);
   void ExtractCellReferences(int entry, Cell* cell);
+  void ExtractWeakCellReferences(int entry, WeakCell* weak_cell);
   void ExtractPropertyCellReferences(int entry, PropertyCell* cell);
   void ExtractAllocationSiteReferences(int entry, AllocationSite* site);
   void ExtractJSArrayBufferReferences(int entry, JSArrayBuffer* buffer);