[parser] Refactor some CHECK_OK calls

src/parsing/preparser.h

Index: src/parsing/preparser.h
diff --git a/src/parsing/preparser.h b/src/parsing/preparser.h
index c246fb14a68a7f195ac4dffc7fc34245edd2f009..9704b929dcbe201b33dbfc7aec30632105800fa4 100644
--- a/src/parsing/preparser.h
+++ b/src/parsing/preparser.h
@@ -759,6 +759,9 @@ class PreParserTraits {
                        const char* arg = NULL,
                        ParseErrorType error_type = kSyntaxError);
 
+  // A dummy function, just useful as an argument to CHECK_OK_CUSTOM.
+  static void Void() {}
+
   // "null" return type creators.
   static PreParserIdentifier EmptyIdentifier() {
     return PreParserIdentifier::Default();