ClangTidy fixes

Change-Id: Iae5a6b0067c726a5c5f6a88acee15a574cb46be6

internal/ceres/dynamic_cost_function_to_functor.cc

diff --git a/internal/ceres/dynamic_cost_function_to_functor.cc b/internal/ceres/dynamic_cost_function_to_functor.cc
index 42e8fac..f6e1a62 100644
--- a/internal/ceres/dynamic_cost_function_to_functor.cc
+++ b/internal/ceres/dynamic_cost_function_to_functor.cc
@@ -29,6 +29,7 @@
 // Author: sameeragarwal@google.com (Sameer Agarwal)
 //         dgossow@google.com (David Gossow)
 
+#include "ceres/cost_function.h"
 #include "ceres/dynamic_cost_function_to_functor.h"
 
 #include <memory>