Merge to upstream r225300.

Change-Id: I2b23715db9ac129ff80aa78ad5824db0a4d6fbb3

test/std/utilities/time/microseconds.pass.cpp

@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <chrono>
+
+// typedef duration<signed integral type of at least 55 bits, micro> microseconds;
+
+#include <chrono>
+#include <type_traits>
+#include <limits>
+
+int main()
+{
+    typedef std::chrono::microseconds D;
+    typedef D::rep Rep;
+    typedef D::period Period;
+    static_assert(std::is_signed<Rep>::value, "");
+    static_assert(std::is_integral<Rep>::value, "");
+    static_assert(std::numeric_limits<Rep>::digits >= 54, "");
+    static_assert((std::is_same<Period, std::micro>::value), "");
+}