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

src/js/string.js

Index: src/js/string.js
diff --git a/src/js/string.js b/src/js/string.js
index 489ff983f787c25b9800e969c3ba3ba45e317f33..d58a91883e6d30b01158a5ff3a6a15790a6c05af 100644
--- a/src/js/string.js
+++ b/src/js/string.js
@@ -843,15 +843,21 @@ function StringSup() {
   return "<sup>" + TO_STRING(this) + "</sup>";
 }
 
-// ES6 draft 01-20-14, section 21.1.3.13
+// ES6, section 21.1.3.13
 function StringRepeat(count) {
   CHECK_OBJECT_COERCIBLE(this, "String.prototype.repeat");
 
   var s = TO_STRING(this);
   var n = TO_INTEGER(count);
+
+  if (n < 0 || n === INFINITY) throw MakeRangeError(kInvalidCountValue);
+
+  // Early return to allow an arbitrarily-large repeat of the empty string.
+  if (s.length === 0) return "";
+
   // The maximum string length is stored in a smi, so a longer repeat
   // must result in a range error.
-  if (n < 0 || n > %_MaxSmi()) throw MakeRangeError(kInvalidCountValue);
+  if (n > %_MaxSmi()) throw MakeRangeError(kInvalidCountValue);
 
   var r = "";
   while (true) {