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 2de53ac0ec890695eeb2c951099d7c112f146f50..2b4d0a47363225a08ce38c27329367c0934e1aa3 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,