Implementing erase/erase_if functions from library fundamentals ts:

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 ae444c2c8e21c38ebec295ee023a365b84b3e057..348d942a98150459e7e675587b5f6e19333922f4 100644
--- a/base/containers/flat_set.h
+++ b/base/containers/flat_set.h
@@ -10,6 +10,8 @@
 #include <utility>
 #include <vector>
 
+#include "base/stl_util.h"
+
 namespace base {
 
 // Overview:
@@ -657,6 +659,14 @@ void flat_set<Key, Compare>::swap(flat_set& other) {
   std::swap(impl_, other.impl_);
 }
 
+// ----------------------------------------------------------------------------
+// Free functions.
+
+template <typename Key, typename Compare, typename Predicate>
+void STLEraseIf(base::flat_set<Key, Compare>& container, Predicate pred) {
+  STLEraseRemoveIf(container, pred);
+}
+
 }  // namespace  base
 
 #endif  // BASE_CONTAINERS_FLAT_SET_H_