Add a missing header to context_impl.cc

Change-Id: I7b6c564ac67926e91543a96bfd6362471de775c8

internal/ceres/context_impl.cc

diff --git a/internal/ceres/context_impl.cc b/internal/ceres/context_impl.cc
index 073dc7a..fac3281 100644
--- a/internal/ceres/context_impl.cc
+++ b/internal/ceres/context_impl.cc
@@ -32,6 +32,8 @@
 
 #include <string>
 
+#include "absl/log/check.h"
+#include "absl/log/log.h"
 #include "ceres/internal/config.h"
 #include "ceres/stringprintf.h"
 #include "ceres/wall_time.h"