[counting_allocator] Chrome changes.

base/containers/flat_set.h

Index: base/containers/flat_set.h
diff --git a/base/containers/flat_set.h b/base/containers/flat_set.h
index aa7e52eddbdfca8758ae32a22479ccccd046f7cd..5b6c9ed0fdbbd9737c130ebb0dfd004aa833fce9 100644
--- a/base/containers/flat_set.h
+++ b/base/containers/flat_set.h
@@ -85,7 +85,7 @@ template <class Key, class Compare = std::less<Key>>
 // Requires: Key is Movable, Compare is a StrictWeakOrdering on Key.
 class flat_set {
  private:
-  using underlying_type = std::vector<Key>;
+  using underlying_type = std::vector<Key, std::counting_allocator<Key, std::allocation_group::base_flat_set>>;
 
  public:
   // --------------------------------------------------------------------------