Implement the function.sent proposal.

src/parsing/preparser.h

Index: src/parsing/preparser.h
diff --git a/src/parsing/preparser.h b/src/parsing/preparser.h
index a477e1a52eacd0bb09d1c660d6e3659712760e7b..976fa7cfe7dbaf39600f605e9b01d9f538082502 100644
--- a/src/parsing/preparser.h
+++ b/src/parsing/preparser.h
@@ -798,6 +798,12 @@ class PreParserTraits {
     return PreParserExpression::Default();
   }
 
+  static PreParserExpression FunctionSentExpression(Scope* scope,
+                                                    PreParserFactory* factory,
+                                                    int pos) {
+    return PreParserExpression::Default();
+  }
+
   static PreParserExpression DefaultConstructor(bool call_super, Scope* scope,
                                                 int pos, int end_pos) {
     return PreParserExpression::Default();