Add a missing include

Change-Id: I3c7e43e053366f3d3c38484b65025285d771f330

internal/ceres/block_jacobi_preconditioner_benchmark.cc

diff --git a/internal/ceres/block_jacobi_preconditioner_benchmark.cc b/internal/ceres/block_jacobi_preconditioner_benchmark.cc
index 90cab9e..1d8ad10 100644
--- a/internal/ceres/block_jacobi_preconditioner_benchmark.cc
+++ b/internal/ceres/block_jacobi_preconditioner_benchmark.cc
@@ -29,6 +29,7 @@
 // Authors: sameeragarwal@google.com (Sameer Agarwal)
 
 #include <memory>
+#include <random>
 
 #include "Eigen/Dense"
 #include "benchmark/benchmark.h"