WIP [esnext] implement async iteration proposal

src/parsing/parser.h

Index: src/parsing/parser.h
diff --git a/src/parsing/parser.h b/src/parsing/parser.h
index 45ef959ed44644d38db9b75ae6a459bc676f51b9..3dada7f00e852b74c2ef87395d1d9f78255e5870 100644
--- a/src/parsing/parser.h
+++ b/src/parsing/parser.h
@@ -449,6 +449,8 @@ class V8_EXPORT_PRIVATE Parser : public NON_EXPORTED_BASE(ParserBase<Parser>) {
   //     %ThrowIteratorResultNotAnObject(result)
   Expression* BuildIteratorNextResult(Expression* iterator, Variable* result,
                                       int pos);
+  Expression* AwaitIteratorNextResult(Expression* iterator, Variable* result,
+                                      int pos);
 
   // Initialize the components of a for-in / for-of statement.
   Statement* InitializeForEachStatement(ForEachStatement* stmt,
@@ -458,6 +460,9 @@ class V8_EXPORT_PRIVATE Parser : public NON_EXPORTED_BASE(ParserBase<Parser>) {
                                       Expression* iterable, Statement* body,
                                       bool finalize,
                                       int next_result_pos = kNoSourcePosition);
+  Statement* InitializeForAwaitOfStatement(
+      ForEachStatement* for_of, Expression* each, Expression* iterable,
+      Statement* body, bool finalize, int next_result_pos = kNoSourcePosition);
   Block* RewriteForVarInLegacy(const ForInfo& for_info);
   void DesugarBindingInForEachStatement(ForInfo* for_info, Block** body_block,
                                         Expression** each_variable, bool* ok);
@@ -639,6 +644,8 @@ class V8_EXPORT_PRIVATE Parser : public NON_EXPORTED_BASE(ParserBase<Parser>) {
 
   Statement* FinalizeForOfStatement(ForOfStatement* loop, Variable* completion,
                                     int pos);
+  Statement* FinalizeForAwaitOfStatement(ForOfStatement* loop,
+                                         Variable* completion, int pos);
   void BuildIteratorClose(ZoneList<Statement*>* statements, Variable* iterator,
                           Variable* input, Variable* output);
   void BuildIteratorCloseForCompletion(Scope* scope,