[builtins] Move StringIncludes to a builtin.

test/mjsunit/es6/string-includes.js

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 assertEquals(1, String.prototype.includes.length);
 
+var s = 'a';
+assertFalse(s.includes(null));
+assertFalse(s.includes(undefined));
+

[Franzi, 2016/10/10 12:58:58]

Can we add assertFalse(s.includes()); just to prevent mistakes in the future?

 var reString = "asdf[a-z]+(asdf)?";
 assertTrue(reString.includes("[a-z]+"));
 assertTrue(reString.includes("(asdf)?"));
 
 // Random greek letters
 var twoByteString = "\u039a\u0391\u03a3\u03a3\u0395";
 
 // Test single char pattern
 assertTrue(twoByteString.includes("\u039a"), "Lamda");
 assertTrue(twoByteString.includes("\u0391"), "Alpha");
@@ skipping 123 matching lines @@
 assertThrows("String.prototype.includes.apply({ 'toString': function() { " +
   "return 'abc'; } }, [/./])", TypeError);
 
 // includes does its brand checks with Symbol.match
 var re = /./;
 assertThrows(function() {
   "".includes(re);
 }, TypeError);
 re[Symbol.match] = false;
 assertEquals(false, "".includes(re));