Applied constexpr to <chrono>.

llvm-svn: 160184
diff --git a/libcxx/test/utilities/time/time.duration/time.duration.cons/default.pass.cpp b/libcxx/test/utilities/time/time.duration/time.duration.cons/default.pass.cpp
index 6e048b2..837f437 100644
--- a/libcxx/test/utilities/time/time.duration/time.duration.cons/default.pass.cpp
+++ b/libcxx/test/utilities/time/time.duration/time.duration.cons/default.pass.cpp
@@ -26,6 +26,10 @@
 {
     D d;
     assert(d.count() == typename D::rep());
+#ifndef _LIBCPP_HAS_NO_CONSTEXPR
+    constexpr D d2;
+    static_assert(d2.count() == typename D::rep(), "");
+#endif
 }
 
 int main()