Fix missing declaration warning in autodiff_manifold_test

Change-Id: I33326faaf3f204db5e9e255d87c82d83ec4b710f

internal/ceres/autodiff_manifold_test.cc

diff --git a/internal/ceres/autodiff_manifold_test.cc b/internal/ceres/autodiff_manifold_test.cc
index b85d244..01820c8 100644
--- a/internal/ceres/autodiff_manifold_test.cc
+++ b/internal/ceres/autodiff_manifold_test.cc
@@ -40,9 +40,19 @@
 namespace ceres {
 namespace internal {
 
+namespace {
+
 constexpr int kNumTrials = 1000;
 constexpr double kTolerance = 1e-9;
 
+Vector RandomQuaternion() {
+  Vector x = Vector::Random(4);
+  x.normalize();
+  return x;
+}
+
+}  // namespace
+
 struct EuclideanFunctor {
   template <typename T>
   bool Plus(const T* x, const T* delta, T* x_plus_delta) const {
@@ -245,12 +255,6 @@
   return true;
 }
 
-Vector RandomQuaternion() {
-  Vector x = Vector::Random(4);
-  x.normalize();
-  return x;
-}
-
 TEST(AutoDiffManifoldTest, QuaternionGenericDelta) {
   AutoDiffManifold<QuaternionFunctor, 4, 3> manifold;
   for (int trial = 0; trial < kNumTrials; ++trial) {