Revert "Revert "Update aosp/master libcxx rebase to r263688""

This reverts commit 1d4a1edbc7.

Change-Id: I2909937fe582f2c5552bc86e7f4d2d5cff0de0aa

test/std/input.output/iostreams.base/ios/basic.ios.members/narrow.pass.cpp

@@ -0,0 +1,24 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+// <ios>
+
+// template <class charT, class traits> class basic_ios
+
+// char narrow(char_type c, char dfault) const;
+
+#include <ios>
+#include <cassert>
+
+int main()
+{
+    const std::ios ios(0);
+    assert(ios.narrow('c', '*') == 'c');
+    assert(ios.narrow('\xFE', '*') == '*');
+}