[builtins] move String.prototype[@@iterator] to C++ builtin

src/factory.cc

Index: src/factory.cc
diff --git a/src/factory.cc b/src/factory.cc
index f7e1c746dd49f79fe31d6ffbb11aab5f24785557..c49ead268b0239cab2ae7a9107e7b36f09a31694 100644
--- a/src/factory.cc
+++ b/src/factory.cc
@@ -600,6 +600,19 @@ MaybeHandle<String> Factory::NewConsString(Handle<String> left,
   return result;
 }
 
+Handle<String> Factory::NewSurrogatePairString(uint16_t lead, uint16_t trail) {
+  DCHECK_GE(lead, 0xD800);
+  DCHECK_LE(lead, 0xDBFF);
+  DCHECK_GE(trail, 0xDC00);
+  DCHECK_LE(trail, 0xDFFF);
+
+  Handle<SeqTwoByteString> str =
+      isolate()->factory()->NewRawTwoByteString(2).ToHandleChecked();
+  uc16* dest = str->GetChars();
+  dest[0] = lead;
+  dest[1] = trail;
+  return str;
+}
 
 Handle<String> Factory::NewProperSubString(Handle<String> str,
                                            int begin,
@@ -734,6 +747,17 @@ Handle<ExternalOneByteString> Factory::NewNativeSourceString(
   return external_string;
 }
 
+Handle<JSStringIterator> Factory::NewJSStringIterator(Handle<String> string) {
+  Handle<Map> map(isolate()->native_context()->string_iterator_map(),
+                  isolate());
+  Handle<String> flat_string = String::Flatten(string);
+  Handle<JSStringIterator> iterator =
+      Handle<JSStringIterator>::cast(NewJSObjectFromMap(map));
+  iterator->set_string(*flat_string);
+  iterator->set_index(0);
+
+  return iterator;
+}
 
 Handle<Symbol> Factory::NewSymbol() {
   CALL_HEAP_FUNCTION(
@@ -1732,6 +1756,15 @@ Handle<JSDataView> Factory::NewJSDataView() {
       JSDataView);
 }
 
+Handle<JSIteratorResult> Factory::NewJSIteratorResult(Handle<Object> value,
+                                                      bool done) {
+  Handle<Map> map(isolate()->native_context()->iterator_result_map());
+  Handle<JSIteratorResult> js_iter_result =
+      Handle<JSIteratorResult>::cast(NewJSObjectFromMap(map));
+  js_iter_result->set_value(*value);
+  js_iter_result->set_done(*ToBoolean(done));
+  return js_iter_result;
+}
 
 Handle<JSMap> Factory::NewJSMap() {
   Handle<Map> map(isolate()->native_context()->js_map_map());