Implement std::string_view as described in http://wg21.link/P0254R1. Reviewed as https://reviews.llvm.org/D21459

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@276238 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/strings/basic.string/string.cons/string_view.fail.cpp

@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+// <string>
+
+// explicit basic_string(basic_string_view<CharT, traits> sv, const Allocator& a = Allocator());
+
+#include <string>
+#include <string_view>
+
+void foo ( const string &s ) {}
+
+int main()
+{
+	std::string_view sv = "ABCDE";
+	foo(sv);	// requires implicit conversion from string_view to string
+}