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

This lets us pass one test262 test (and seems to match what other
implementations do to handle this case).

R=littledan@chromium.org
BUG=v8:4362
LOG=n

Review URL: https://codereview.chromium.org/1454543003

Cr-Commit-Position: refs/heads/master@{#32155}

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) {

test/mjsunit/es6/string-repeat.js

@@ -65,6 +65,12 @@ 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";

test/test262/test262.status

@@ -368,9 +368,6 @@
   # https://code.google.com/p/v8/issues/detail?id=4361
   'intl402/Collator/10.1.1_a': [FAIL],
 
-  # https://code.google.com/p/v8/issues/detail?id=4362
-  'built-ins/String/prototype/repeat/empty-string-returns-empty': [PASS, FAIL],
-
   # https://code.google.com/p/v8/issues/detail?id=4447
   'built-ins/Function/prototype/Symbol.hasInstance/*': [SKIP],
   'built-ins/Symbol/hasInstance/prop-desc': [FAIL],