Implement the function.sent proposal.

src/parsing/parser.h

Index: src/parsing/parser.h
diff --git a/src/parsing/parser.h b/src/parsing/parser.h
index 182916d504fbc2f64c06138e2eec4995d16743db..c37953f04ad3c24480d8f57303e2ade4340ae02c 100644
--- a/src/parsing/parser.h
+++ b/src/parsing/parser.h
@@ -513,6 +513,8 @@ class ParserTraits {
                                  int pos);
   Expression* NewTargetExpression(Scope* scope, AstNodeFactory* factory,
                                   int pos);
+  Expression* FunctionSentExpression(Scope* scope, AstNodeFactory* factory,
+                                     int pos);
   Expression* DefaultConstructor(bool call_super, Scope* scope, int pos,
                                  int end_pos, LanguageMode language_mode);
   Literal* ExpressionFromLiteral(Token::Value token, int pos, Scanner* scanner,