[builtins] Move StringIncludes to a builtin.

test/mjsunit/es6/string-includes.js

Index: test/mjsunit/es6/string-includes.js
diff --git a/test/mjsunit/es6/string-includes.js b/test/mjsunit/es6/string-includes.js
index c825ffdc6852496f332f28b1d70b9ef01d1ace24..60a7ddd6858e3349d4e0d2e5163b7c2a1bb120ae 100644
--- a/test/mjsunit/es6/string-includes.js
+++ b/test/mjsunit/es6/string-includes.js
@@ -27,6 +27,11 @@
 
 assertEquals(1, String.prototype.includes.length);
 
+var s = 'a';
+assertFalse(s.includes(null));
+assertFalse(s.includes(undefined));
+assertFalse(s.includes());
+
 var reString = "asdf[a-z]+(asdf)?";
 assertTrue(reString.includes("[a-z]+"));
 assertTrue(reString.includes("(asdf)?"));