Add missing include headers in Balsa.

PiperOrigin-RevId: 448569314
diff --git a/quiche/balsa/balsa_frame.h b/quiche/balsa/balsa_frame.h
index c9bca84..5b569ea 100644
--- a/quiche/balsa/balsa_frame.h
+++ b/quiche/balsa/balsa_frame.h
@@ -10,6 +10,7 @@
 #include <utility>
 #include <vector>
 
+#include "absl/container/flat_hash_map.h"
 #include "quiche/balsa/balsa_enums.h"
 #include "quiche/balsa/balsa_headers.h"
 #include "quiche/balsa/balsa_visitor_interface.h"
diff --git a/quiche/balsa/balsa_headers.h b/quiche/balsa/balsa_headers.h
index 9302dad..a730649 100644
--- a/quiche/balsa/balsa_headers.h
+++ b/quiche/balsa/balsa_headers.h
@@ -17,6 +17,8 @@
 #include <utility>
 #include <vector>
 
+#include "absl/container/flat_hash_map.h"
+#include "absl/container/flat_hash_set.h"
 #include "absl/memory/memory.h"
 #include "absl/strings/ascii.h"
 #include "absl/strings/match.h"