Reland "[builtins] migrate C++ String Iterator builtins to baseline TurboFan"

test/mjsunit/es6/string-iterator.js

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 function TestStringPrototypeIterator() {
   assertTrue(String.prototype.hasOwnProperty(Symbol.iterator));
   assertFalse("".hasOwnProperty(Symbol.iterator));
   assertFalse("".propertyIsEnumerable(Symbol.iterator));
 }
 TestStringPrototypeIterator();
@@ skipping 74 matching lines @@
 TestForOf();
 
 
 function TestNonOwnSlots() {
   var iterator = ""[Symbol.iterator]();
   var object = {__proto__: iterator};
 
   assertThrows(function() { object.next(); }, TypeError);
 }
 TestNonOwnSlots();
+
+
+function TestSlicedStringRegression() {
+  var long_string = "abcdefhijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
+  var sliced_string = long_string.substring(1);
+  var iterator = sliced_string[Symbol.iterator]();
+}
+TestSlicedStringRegression();