WIP [esnext] implement async iteration proposal

src/parsing/preparser.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_PARSING_PREPARSER_H
 #define V8_PARSING_PREPARSER_H
 
 #include "src/ast/ast.h"
 #include "src/ast/scopes.h"
 #include "src/parsing/parser-base.h"
@@ skipping 1264 matching lines @@
   }
 
   V8_INLINE PreParserStatement
   InitializeForEachStatement(PreParserStatement stmt, PreParserExpression each,
                              PreParserExpression subject,
                              PreParserStatement body, int each_keyword_pos) {
     MarkExpressionAsAssigned(each);
     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();
   }
 
   V8_INLINE void DesugarBindingInForEachStatement(
       ForInfo* for_info, PreParserStatement* body_block,
       PreParserExpression* each_variable, bool* ok) {
     if (track_unresolved_variables_) {
       DCHECK(for_info->parsing_result.declarations.length() == 1);
       DeclareAndInitializeVariables(
@@ skipping 338 matching lines @@
     function_state_->NextMaterializedLiteralIndex();
     function_state_->NextMaterializedLiteralIndex();
   }
   return EmptyExpression();
 }
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PARSING_PREPARSER_H