--- a/base/containers/flat_set.h.orig	2017-04-28 14:39:24.143751606 +0000
+++ b/base/containers/flat_set.h	2017-04-28 14:39:33.815953089 +0000
@@ -5,6 +5,8 @@
 #ifndef BASE_CONTAINERS_FLAT_SET_H_
 #define BASE_CONTAINERS_FLAT_SET_H_
 
+#include <functional>
+
 #include "base/containers/flat_tree.h"
 
 namespace base {