[es6] Implement Date.prototype[@@toPrimitive] as C++ builtin.

test/mjsunit/harmony/to-name.js

Index: test/mjsunit/harmony/to-name.js
diff --git a/test/mjsunit/harmony/to-name.js b/test/mjsunit/harmony/to-name.js
index c15bfb5d29a92f28a919e8a2f3688c6c8f58729e..f947ef77b94ccafb3f121b61d7f22652d0f0568b 100644
--- a/test/mjsunit/harmony/to-name.js
+++ b/test/mjsunit/harmony/to-name.js
@@ -48,3 +48,7 @@ var d = {
 };
 assertEquals("string", %ToName(d));
 assertEquals("string", %_ToName(d));
+
+var e = new Date(0);
+assertEquals("Thu Jan 01 1970 01:00:00 GMT+0100 (CET)", %ToName(e));
+assertEquals("Thu Jan 01 1970 01:00:00 GMT+0100 (CET)", %_ToName(e));