Use FastaMessage instead of String. Part 1.

pkg/front_end/lib/src/fasta/source/diet_parser.dart

Index: pkg/front_end/lib/src/fasta/source/diet_parser.dart
diff --git a/pkg/front_end/lib/src/fasta/source/diet_parser.dart b/pkg/front_end/lib/src/fasta/source/diet_parser.dart
index 7d8a8e526df68797b7c207236802d3738f6d9e0c..5addc0708d1d035ce1dc0a9e411cc202dd8cec27 100644
--- a/pkg/front_end/lib/src/fasta/source/diet_parser.dart
+++ b/pkg/front_end/lib/src/fasta/source/diet_parser.dart
@@ -26,7 +26,7 @@ class DietParser extends ClassMemberParser {
     listener.beginOptionalFormalParameters(token);
     if (!optional('(', token)) {
       if (optional(';', token)) {
-        reportRecoverableErrorCode(token, codeExpectedOpenParens);
+        reportRecoverableError(token, codeExpectedOpenParens);
         return token;
       }
       return reportUnexpectedToken(token).next;