Update mutex to include scoped_lock stubs

Author: lcartey

cpp/common/test/includes/standard-library/mutex.h

@@ -1,6 +1,6 @@
 #ifndef _GHLIBCPP_MUTEX
 #define _GHLIBCPP_MUTEX
-#include "chrono.h"
+#include <chrono>
 
 namespace std {
 
@@ -77,6 +77,14 @@ template <typename Mutex> class lock_guard {
   mutex_type &_m;
 };
 
+template <class... MutexTypes> class scoped_lock {
+public:
+  explicit scoped_lock(MutexTypes &...m);
+  scoped_lock(const scoped_lock &) = delete;
+  scoped_lock &operator=(const scoped_lock &) = delete;
+  ~scoped_lock();
+};
+
 } // namespace std
 
 #endif // _GHLIBCPP_MUTEX