Merge to upstream r225300.

Change-Id: I2b23715db9ac129ff80aa78ad5824db0a4d6fbb3

test/std/thread/thread.threads/thread.thread.class/thread.thread.id/assign.pass.cpp

@@ -0,0 +1,29 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+//
+// UNSUPPORTED: libcpp-has-no-threads
+
+// <thread>
+
+// class thread::id
+
+// id& operator=(const id&) = default;
+
+#include <thread>
+#include <cassert>
+
+int main()
+{
+    std::thread::id id0;
+    std::thread::id id1;
+    id1 = id0;
+    assert(id1 == id0);
+    id1 = std::this_thread::get_id();
+    assert(id1 != id0);
+}