[es6] Allow any valid repeat of empty string in String.prototype.repeat

test/mjsunit/es6/string-repeat.js

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 47 matching lines @@
 assertEquals("", "".repeat(5));
 assertEquals("", "abc".repeat(0));
 assertEquals("abcabc", "abc".repeat(2.0));
 
 assertEquals("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa", "a".repeat(37));
 assertThrows('"a".repeat(-1)', RangeError);
 assertThrows('"a".repeat(Number.POSITIVE_INFINITY)', RangeError);
 assertThrows('"a".repeat(Math.pow(2, 30))', RangeError);
 assertThrows('"a".repeat(Math.pow(2, 40))', RangeError);
 
+// Handling empty strings
+assertThrows('"".repeat(-1)', RangeError);
+assertThrows('"".repeat(Number.POSITIVE_INFINITY)', RangeError);
+assertEquals("", "".repeat(Math.pow(2, 30)));
+assertEquals("", "".repeat(Math.pow(2, 40)));
+
 var myobj = {
   toString: function() {
     return "abc";
   },
   repeat : String.prototype.repeat
 };
 assertEquals("abc", myobj.repeat(1));
 assertEquals("abcabc", myobj.repeat(2));