Add remaining @@toStringTag symbols to builtins

src/collection-iterator.js

Index: src/collection-iterator.js
diff --git a/src/collection-iterator.js b/src/collection-iterator.js
index 2bccc8d7a2c0c4a66740811a4504f6ac3a5d3849..92d45a9cd2668dae053257f994e81966be8a8ecb 100644
--- a/src/collection-iterator.js
+++ b/src/collection-iterator.js
@@ -77,6 +77,8 @@ function SetUpSetIterator() {
   %FunctionSetName(SetIteratorSymbolIterator, '[Symbol.iterator]');
   %AddNamedProperty(SetIterator.prototype, symbolIterator,
       SetIteratorSymbolIterator, DONT_ENUM);
+  %AddNamedProperty(SetIterator.prototype, symbolToStringTag,
+      "Set Iterator", READ_ONLY | DONT_ENUM);
 }
 
 SetUpSetIterator();
@@ -174,6 +176,8 @@ function SetUpMapIterator() {
   %FunctionSetName(MapIteratorSymbolIterator, '[Symbol.iterator]');
   %AddNamedProperty(MapIterator.prototype, symbolIterator,
       MapIteratorSymbolIterator, DONT_ENUM);
+  %AddNamedProperty(MapIterator.prototype, symbolToStringTag,
+      "Map Iterator", READ_ONLY | DONT_ENUM);
 }
 
 SetUpMapIterator();