[esnext] prototype runtime implementation for async functions

src/parsing/preparser.cc

Index: src/parsing/preparser.cc
diff --git a/src/parsing/preparser.cc b/src/parsing/preparser.cc
index b09488715464d470988788edc0d7ffde93a49509..d7ba88cc6049d2bfb7d0fa2c663e362a99c44c12 100644
--- a/src/parsing/preparser.cc
+++ b/src/parsing/preparser.cc
@@ -121,6 +121,7 @@ PreParser::PreParseResult PreParser::PreParseLazyFunction(
   DCHECK_EQ(Token::LBRACE, scanner()->current_token());
   bool ok = true;
   int start_position = peek_position();
+  function_state.set_parse_phase(FunctionParsePhase::FunctionBody);
   ParseLazyFunctionLiteralBody(&ok, bookmark);
   use_counts_ = nullptr;
   if (bookmark && bookmark->HasBeenReset()) {
@@ -1105,6 +1106,7 @@ PreParser::Expression PreParser::ParseFunctionLiteral(
   int start_position = scanner()->location().beg_pos;
   function_scope->set_start_position(start_position);
   PreParserFormalParameters formals(function_scope);
+  function_state.set_parse_phase(FunctionParsePhase::FormalParameters);
   ParseFormalParameterList(&formals, &formals_classifier, CHECK_OK);
   Expect(Token::RPAREN, CHECK_OK);
   int formals_end_position = scanner()->location().end_pos;
@@ -1117,6 +1119,7 @@ PreParser::Expression PreParser::ParseFunctionLiteral(
   bool is_lazily_parsed = (outer_is_script_scope && allow_lazy() &&
                            !function_state_->this_function_is_parenthesized());
 
+  function_state.set_parse_phase(FunctionParsePhase::FunctionBody);
   Expect(Token::LBRACE, CHECK_OK);
   if (is_lazily_parsed) {
     ParseLazyFunctionLiteralBody(CHECK_OK);
@@ -1290,6 +1293,19 @@ PreParserExpression PreParser::ParseDoExpression(bool* ok) {
   return PreParserExpression::Default();
 }
 
+void PreParserTraits::ParseAsyncArrowSingleExpressionBody(
+    PreParserStatementList body, bool accept_IN,
+    Type::ExpressionClassifier* classifier, int pos, bool* ok) {
+  Scope* scope = pre_parser_->scope_;
+  scope->ForceContextAllocation();
+
+  PreParserExpression return_value =
+      pre_parser_->ParseAssignmentExpression(accept_IN, classifier, ok);
+  if (!*ok) return;
+
+  body->Add(PreParserStatement::ExpressionStatement(return_value), zone());
+}
+
 #undef CHECK_OK