Modernise code to use std::make_unique

Generated by clang-tidy.

Test: m checkbuild
Change-Id: Idb24960d9326c0d94ab5d04b18deb0894d23da9f
diff --git a/runtime/monitor_test.cc b/runtime/monitor_test.cc
index 8610899..8ddd50f 100644
--- a/runtime/monitor_test.cc
+++ b/runtime/monitor_test.cc
@@ -16,6 +16,7 @@
 
 #include "monitor.h"
 
+#include <memory>
 #include <string>
 
 #include "base/atomic.h"
@@ -251,8 +252,8 @@
                                                                               "hello, world!"));
 
   // Create the barrier used to synchronize.
-  test->barrier_ = std::unique_ptr<Barrier>(new Barrier(2));
-  test->complete_barrier_ = std::unique_ptr<Barrier>(new Barrier(3));
+  test->barrier_ = std::make_unique<Barrier>(2);
+  test->complete_barrier_ = std::make_unique<Barrier>(3);
   test->completed_ = false;
 
   // Our job: Fill the heap, then try Wait.