[parser] Refactor some CHECK_OK calls

src/parsing/parser.h

Index: src/parsing/parser.h
diff --git a/src/parsing/parser.h b/src/parsing/parser.h
index 76611dfae55bdc4fe6e92aa2fc2c06b574d5f983..237c851e5691a165bbf4f130051328a45ef8af7f 100644
--- a/src/parsing/parser.h
+++ b/src/parsing/parser.h
@@ -475,6 +475,9 @@ class ParserTraits {
                        const AstRawString* arg,
                        ParseErrorType error_type = kSyntaxError);
 
+  // A dummy function, just useful as an argument to CHECK_OK_CUSTOM.
+  static void Void() {}
+
   // "null" return type creators.
   static const AstRawString* EmptyIdentifier() {
     return NULL;