Heap profiler: reduce heap snapshots size.

src/list.h

Index: src/list.h
diff --git a/src/list.h b/src/list.h
index d3c2767a53bc885f978b88106d6350e9d10d581a..9abf61ce557918dd6f907ad8edb8c0ca377591c9 100644
--- a/src/list.h
+++ b/src/list.h
@@ -117,6 +117,8 @@ class List {
 
   // Iterate through all list entries, starting at index 0.
   void Iterate(void (*callback)(T* x));
+  template<class Visitor>
+  void Iterate(Visitor* visitor);
 
   // Sort all list entries (using QuickSort)
   void Sort(int (*cmp)(const T* x, const T* y));