Make all global private symbols own symbols.

src/string-iterator.js

Index: src/string-iterator.js
diff --git a/src/string-iterator.js b/src/string-iterator.js
index 7222885a56f465931980d646a277ea9c69cc1abf..dc2aeee2c7c38c9a56dd099ef33b511420ef5333 100644
--- a/src/string-iterator.js
+++ b/src/string-iterator.js
@@ -11,8 +11,10 @@
 
 
 var stringIteratorIteratedStringSymbol =
-    GLOBAL_PRIVATE("StringIterator#iteratedString");
-var stringIteratorNextIndexSymbol = GLOBAL_PRIVATE("StringIterator#next");
+    GLOBAL_PRIVATE_OWN("StringIterator#iteratedString");
+var stringIteratorNextIndexSymbol = GLOBAL_PRIVATE_OWN("StringIterator#next");
+
+var stringEndOfIterationMarker = new $Object();
 
 
 function StringIterator() {}
@@ -38,13 +40,13 @@ function StringIteratorIterator() {
 function StringIteratorNext() {
   var iterator = ToObject(this);
 
-  if (!HAS_PRIVATE(iterator, stringIteratorIteratedStringSymbol)) {
+  if (IS_PRIVATE_OWN_UNDEFINED(iterator, stringIteratorIteratedStringSymbol)) {
     throw MakeTypeError('incompatible_method_receiver',
                         ['String Iterator.prototype.next']);
   }
 
   var s = GET_PRIVATE(iterator, stringIteratorIteratedStringSymbol);
-  if (IS_UNDEFINED(s)) {
+  if (s === stringEndOfIterationMarker) {
     return CreateIteratorResultObject(UNDEFINED, true);
   }
 
@@ -52,7 +54,8 @@ function StringIteratorNext() {
   var length = TO_UINT32(s.length);
 
   if (position >= length) {
-    SET_PRIVATE(iterator, stringIteratorIteratedStringSymbol, UNDEFINED);
+    SET_PRIVATE(iterator, stringIteratorIteratedStringSymbol,
+                stringEndOfIterationMarker);
     return CreateIteratorResultObject(UNDEFINED, true);
   }