Add debug mirror support for ES6 Map/Set iterators.

src/factory.h

Index: src/factory.h
diff --git a/src/factory.h b/src/factory.h
index e9972cc13a8a96613a3bc4102745bb43c503045f..d7e60014db1c068f1a2b92e2c58bda48b8b8bb32 100644
--- a/src/factory.h
+++ b/src/factory.h
@@ -445,6 +445,9 @@ class Factory FINAL {
   Handle<JSDataView> NewJSDataView(Handle<JSArrayBuffer> buffer,
                                    size_t byte_offset, size_t byte_length);
 
+  Handle<JSMapIterator> NewJSMapIterator();
+  Handle<JSSetIterator> NewJSSetIterator();
+
   // Allocates a Harmony proxy.
   Handle<JSProxy> NewJSProxy(Handle<Object> handler, Handle<Object> prototype);