WIP [esnext] implement async iteration proposal

src/parsing/preparser.h

Index: src/parsing/preparser.h
diff --git a/src/parsing/preparser.h b/src/parsing/preparser.h
index 1f822a46c3591e7b6922adf095ac8433b4dcf4ab..704c8432c1a58e28e52c9defc63c30ded3d9cb28 100644
--- a/src/parsing/preparser.h
+++ b/src/parsing/preparser.h
@@ -1287,6 +1287,13 @@ class PreParser : public ParserBase<PreParser> {
     return stmt;
   }
 
+  V8_INLINE PreParserStatement InitializeForAwaitOfStatement(
+      PreParserStatement stmt, PreParserExpression each,
+      PreParserExpression subject, PreParserStatement body,
+      int each_keyword_pos) {
+    return stmt;
+  }
+
   V8_INLINE PreParserStatement RewriteForVarInLegacy(const ForInfo& for_info) {
     return PreParserStatement::Null();
   }