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

src/factory.h

Index: src/factory.h
diff --git a/src/factory.h b/src/factory.h
index 964ac555c4e5cce544adb04eb4708d154fdfbb20..6719b59daf17996ad25f32b74de2fa00b11a4a4a 100644
--- a/src/factory.h
+++ b/src/factory.h
@@ -180,6 +180,8 @@ class Factory final {
   MUST_USE_RESULT MaybeHandle<String> NewStringFromTwoByte(
       const ZoneVector<uc16>* str, PretenureFlag pretenure = NOT_TENURED);
 
+  Handle<JSStringIterator> NewJSStringIterator(Handle<String> string);
+
   // Allocates an internalized string in old space based on the character
   // stream.
   Handle<String> NewInternalizedStringFromUtf8(Vector<const char> str,
@@ -221,6 +223,10 @@ class Factory final {
   MUST_USE_RESULT MaybeHandle<String> NewConsString(Handle<String> left,
                                                     Handle<String> right);
 
+  // Create or lookup a single characters tring made up of a utf16 surrogate
+  // pair.
+  Handle<String> NewSurrogatePairString(uint16_t lead, uint16_t trail);
+
   // Create a new string object which holds a proper substring of a string.
   Handle<String> NewProperSubString(Handle<String> str,
                                     int begin,
@@ -508,6 +514,8 @@ class Factory final {
   Handle<JSDataView> NewJSDataView(Handle<JSArrayBuffer> buffer,
                                    size_t byte_offset, size_t byte_length);
 
+  Handle<JSIteratorResult> NewJSIteratorResult(Handle<Object> value, bool done);
+
   Handle<JSMap> NewJSMap();
   Handle<JSSet> NewJSSet();